The involvement of dopamine in the regulation of steroidogenesis in rat ovarian cells

Prefrontal allopregnanolone synergizes with D1 receptor activation to disrupt sensorimotor gating in male Sprague-Dawley rats

RATIONALE

The prepulse inhibition (PPI) of the startle reflex is the best-established index of sensorimotor gating. We documented that the neurosteroid allopregnanolone (AP) is necessary to reduce PPI in response to D₁ dopamine receptor agonists. Since Sprague-Dawley (SD) rats are poorly sensitive to the PPI-disrupting effects of these drugs, we hypothesized that AP might increase this susceptibility.

OBJECTIVES

We tested whether AP is sufficient to increase the vulnerability of SD rats to PPI deficits in response to the D₁ receptor full agonist SKF82958.

METHODS

SD rats were tested for PPI after treatment with SKF82958 (0.05-0.3 mg/kg, SC) in combination with either intraperitoneal (1-10 mg/kg) or intracerebral (0.5 μg/μl/side) AP administration into the medial prefrontal cortex (mPFC) or nucleus accumbens shell. To rule out potential confounds, we measured whether SKF82958 affected the endogenous mPFC levels of AP.

RESULTS

SD rats exhibited marked PPI deficits in response to the combination of systemic and intra-mPFC AP with SKF82958 but not with the D₂ receptor agonist quinpirole (0.3-0.6 mg/kg, SC). SKF82958 did not elevate mPFC levels of AP but enhanced the content of its precursor progesterone. The PPI deficits caused by SKF82958 in combination with AP were opposed by the AP antagonist isoallopregnanolone (10 mg/kg, IP) and the glutamate NMDA receptor positive modulator CIQ (5 mg/kg, IP).

CONCLUSION

These results suggest that AP enables the detrimental effects of D₁ receptor activation on sensorimotor gating. AP antagonism or glutamatergic modulation counters these effects and may have therapeutic potential for neuropsychiatric disorders characterized by gating deficits.

An in vitro study on noradrenergic modulation of final oocyte maturation in the catfish Heteropneustes fossilis

This study was aimed to elucidate in vitro the effects of endogenous catecholamines: dopamine (DA), noradrenaline (NA) and adrenaline (A), and the β-adrenergic blocker propranolol on induction of final oocyte maturation (FOM) in the catfish Heteropneustes fossilis. With this aim, post vitellogenic follicles from sexually mature gravid female catfish were incubated with each of DA, NA and A in a concentration range of 5-250 μM, and propranolol in a concentration range of 1-200 μg/mL at time points varying from 0 to 30 h). Translucent follicles without germinal vesicle (GV) and opaque follicles with GV were scored separately for the calculation of percentage germinal vesicle breakdown (GVBD), an index of FOM. Data were analyzed by one-way ANOVA and were considered statistically significant when P values were less than 0.05. The analysis of the data showed that the incubation with NA only stimulated GVBD in a concentration - and time-dependent manner. Though the incubation with propranolol decreased total follicular cAMP level significantly at and above 10 μg/mL concentrations, a significant effect of the GVBD increase was noticed at 50 μg/mL or higher. However, the 10 μg/mL concentration of propranolol was effective to inhibit the NA-induced GVBD significantly albeit at a low level (39%). The present study suggests that final oocyte maturation is modulated by NA through a β-adrenergic mechanism, implicating a neural control of oocyte maturation and ovulation in teleosts.

Effects of ovarian dopaminergic receptors on ovulation

Hormonal and neural signals regulate the ovarian follicular development. The present study's hypothesis is that the blockade of ovarian dopamine receptors locally will affect follicle development and ovulation. Groups of adult 4-day cyclic rats of the CII-ZV strain on estrus, diestrus-1, diestrus-2, or proestrus day were injected with vehicle, haloperidol (DA2 > DA1 blocker), sulpiride (DA2 blocker), or SCH-23390 (DA1 blocker) into the bursa of both ovaries at 08:00, 13:00, or 20:00 h. Animals were sacrificed the following predicted estrus day. The following treatments blocked ovulation: injecting haloperidol to rats on estrus or diestrus-1 at 8:00, 13:00, or 20:00 h and to rats on diestrus-2 at 08:00, or 20:00 h; injecting SCH-23390 to rats on diestrus-1 at 8:00, 13:00, or 20:00 h; injecting sulpiride to rats on estrus at 20:00 h, diestrus-1 at 08:00, 13:00, or 20:00 h and to rats on diestrus-2 at 08:00 h. In rats treated with any of the dopamine antagonists that blocked ovulation, injecting GnRH at 14.00 h on the next predicted proestrus day restored ovulation. Injecting estradiol benzoate at 14.00 h of the next predicted diestrus-2 restored ovulation in some animals treated with haloperidol on estrus or diestrus-2 and was ineffective in rats treated on diestrus-1. In rats treated with sulpiride or SCH-23390 ovulation occurred in most animals (SCH-23390: 6/8; SPD: 9/12). Present results suggest that dopamine ovarian receptors' participation in regulating follicular development and ovulation varies along the estrus cycle, with their most prominent activity occurring on diestrus-1.

Effect of feeding fermented rice punch on oestrous induction in anoestrous bitches

Introduction

As a consequence of poor productivity caused by a long anoestrous period, considerable research effort has been given to oestrus induction in dogs to enhance the productivity of young dogs and to preserve breeds.

Materials and methods

Oestrus was induced in 30 anoestrous bitches more than three months after the last oestrus. Bitches orally received fermented rice punch with or without bromocriptine once daily for 21 consecutive days. The bitches were divided into two groups (n=10 per group): Group (1) fed fermented rice punch and Group (2) administered bromocriptine (100 µg/kg/day) and fed fermented rice punch.

Results

The concentration of dopamine in fermented rice punch was 47.2 mg/kg (parts per million). Six of 10 (60.0 per cent) and seven of 10 (70.0 per cent) bitches showed pro-oestrual bleeding in Groups 1 and 2, respectively. The mean and median values (min–max) to oestrus induction was not significantly different between Groups 1 and 2 (9.7±7.3, 6.5 (3–22) and 11.3±6.6, 7.9 (5–21) days) after treatment commencement (P>0.05). The pregnancy rate was very similar between Groups 1, 2 (66.0%) and control (66.0, 57.0 and 50.0 per cent). The mean and median values (min–max) of pups per bitch are also not significantly different between Groups 1, 2 and control (7.0±1.8, 7.0 (5–9) and 7.5±2.1, 7.5 (5–10) and 7.0±0, 7.0 (7–7)).

Conclusion

We suggest that rice punch effectively induces oestrus in bitches.

An in vitro study on catecholamine modulation of ovarian steroidogenic activity in the catfish Heteropneustes fossilis

In the present study, α-methylparatyrosine (α-MPT), a tyrosine hydroxylase inhibitor was used to impair ovarian catecholaminergic activity in vitro. The consequent effects on catecholamine (CA) levels were correlated with follicular steroid production. l-dihdroxyphenylalanine (l-DOPA, the precursor of CA) and human gonadotropin (hCG) were supplemented to reverse the effect of α-MPT. The experiments were conducted in two reproductive phases, namely preparatory and pre-spawning phases in female catfish Heteropneustes fossilis. The incubation with α-MPT inhibited ovarian l-DOPA, dopamine (DA), norepinephrine (NE) and epinephrine (EP) levels and the l-DOPA supplementation compensated the inhibitory effect. The level of tyramine (TR) was increased by the α-MPT treatment but inhibited by the l-DOPA supplementation. α-MPT produced stage-specific (seasonal) effects on ovarian estradiol-17β (E2); in the preparatory phase, E2 was decreased significantly at both 12 and 24h and in the pre-spawning phase, the level was stimulated over the respective control groups. The changes were higher at 24h in both phases. l-DOPA and hCG increased the E2 level significantly in the preparatory phase and reversed the inhibitory effect of α-MPT in the co-incubation groups. In the pre-spawning phase, α-MPT-stimulated the E2 level compared to the control groups, which was reversed by l-DOPA, hCG, or by both, in co-incubations. In contrast, the α-MPT treatment decreased progesterone (P4), 17-hydroxyprogesterone and 17,20β-dihydroxy-4-prenen-3-one (17,20β-DP) in a duration-dependent manner while the co-incubations with l-DOPA, hCG, or by both, significantly reversed the inhibitory effect. These results suggest that ovarian CAs (DA, NE and EP) may exert differential and stage-specific effects on E2, inhibition in the preparative phase and stimulation in the pre-spawning phase. The progestin steroids appear to be stimulated by CAs. In conclusion, this study highlights a possible direct/causal functional interaction between CA activity and gonadotropin on steroidogenic activity, and that CAs may be involved in regulating temporal secretion of the hormones through causing the shift in steroidogenic pattern.

Temporal and periovulatory changes in ovarian catecholamines in the catfish Heteropneustes fossilis

A high performance liquid chromatography-fluorescence detection method was employed to demonstrate temporal and periovulatory changes in ovarian catecholamines in the catfish Heteropneustes fossilis. Tyrosine, L-DOPA, dopamine (DA), norepinephrine (NE) and epinephrine showed significant seasonal and diurnal changes during the reproductive cycle. A high concentration of tyrosine was detected, the values increased in day and decreased in night during recrudescence from preparatory to spawning phases. Similarly, L-DOPA increased during the breeding phase giving the day value concentration peak in the spawning phase and the night value peak in the postspawning phase. DA activity or turnover index (calculated as a ratio of DA to 3,4-dihydroxyphenylacetic acid, DOPAC) showed a bimodal pattern with the major activity peak in the postspawning phase and the minor one in the prespawning phase, the spawning phase registered the lowest activity. NE activity or turnover index (ratio of NE to normetanephrine, NME) increased during the recrudescent phase to give the peak in the spawning phase and decreased in the quiescent phase. Epinephrine elicited an inverse relationship in the day-night pattern, the day values increased to the peak in the spawning phase. All the study correlates showed significant periovulatory changes after hCG treatment. DA activity dropped to the nadir at 8h but recovered at 16 and 24h. NE activity showed only a marginal decrease up to 16h but decreased drastically at 24h. Epinephrine levels remained unchanged but only to increase at 24h. The seasonal patterns and periovulatory changes strongly point to important functions for catecholamines in the ovary. The occurrence of tyramine (an invertebrate neurotransmitter) suggests the presence of alternate catecholamine pathway in fish ovary.

Progesterone attenuates cocaine-induced responses

In this review, we summarize literature focused on how progesterone alters cocaine-induced psychomotor, reinforcement, and physiological responses. Clinical studies suggest that progesterone attenuates the subjective effects of cocaine. Similarly, preclinical studies have demonstrated that cocaine-induced reward and psychomotor responses are attenuated after progesterone administration. In rats progesterone also reduces the reinforcement effects of cocaine attenuates acquisition, escalation, reinstatement of cocaine self-administration, and cocaine-seeking behaviors. Progesterone also counteracts the facilitatory effects of estrogen on cocaine self-administration and psychomotor activation. These findings suggest that progesterone has a potential in clinical applications as a treatment for cocaine addiction. Constantly changing progesterone serum levels in female humans and rats affect the female's reinforcement responses to cocaine and may in part contribute to the known sex differences in cocaine responses.

Follicular development and plasma concentrations of LH and prolactin in anestrous female dogs treated with the dopamine agonist cabergoline

The effect of a daily administration of a dopamine agonist (cabergoline, 5 microg/kg) for 4 weeks, starting about 95 days after the end of estrus on follicular development and its relationship with LH and prolactin secretion has been investigated in two groups of anestrous bitches (Beagles and Greyhounds). Pro-estrus was detected in 80% (8/10) of beagles and 50% (3/6) of treated greyhounds. The mean inter-estrus interval of treated animals was 132+/-5.0 and 169+/-7.0 days for beagles and greyhounds, respectively, and in both this differed significantly from the cycle preceding treatment (192+/-9.0 and 198+/-12.0 days) and from that in untreated bitches (194+/-11.0 and 196+/-11.0 days for beagles and greyhounds, respectively (all comparisons at P<0.001). The interval from the beginning of treatment to pro-estrus in responding animals was 13.3+/-1.90 days in beagles and 20.3+/-1.70 days in greyhounds. Cabergoline increased (P<0.001) the length of pro-estrus (10.6+/-0.50 and 11.7+/-0.50 days) in the treated estrus cycle compared to the previous estrus cycle (8.4+/-0.30 and 8.8+/-0.40 days for in beagles and greyhound, respectively). Ovarian enlargement and follicle development was detected by ultrasound in 90% of treated beagles and in 83% of greyhound between the second and third weeks of treatment, but only 80% of beagles and 66% of treated greyhound displayed pro-estrus and estrus. In the treated bitches, mean plasma LH increased (P<0.001) before pro-estrus. There was high variability in mean plasma prolactin levels between animals. These data indicate that the administration of the dopamine agonist cabergoline to anestrous bitches increases mean LH plasma levels and induces follicular development shortly before pro-estrus but this activity is not always followed by pro-estrus and estrus. Finally, prolactin per se does not have a prominent role in the control of folliculogenesis in the bitch.

Estrus induction and synchronization in canids and felids

Indications for estrus induction in the dog and cat include potential missed breeding opportunities or conception failure, the treatment of primary or secondary anestrus, out-of-season breeding (feline) and synchronization of ovulation for embryo transfer programs. Reported methods for estrus induction in bitches and queens include the use of synthetic estrogens (diethylstilbesterol), dopamine agonists (bromocriptine and cabergoline), GnRH agonists (lutrelin, buserelin, fertirelin, deslorelin, and leuprolide), exogenous gonadotropins (LH, FSH, hCG, PMSG, and human menopausal gonadotropin) and opiate antagonists (naloxone). These methods vary widely in efficacy of inducing estrus as well as in the fertility of the induced estrus. The applicability of some of these methods for clinical practice is questionable. This review will summarize published reports on estrus induction in canids and felids, both wild and domestic, and provide an update on research using a long-acting injectable deslorelin preparation in bitches.

Progesterone receptors activation after acute cocaine administration

Cocaine modulates serum levels of progesterone in intact female and male rats, as well as in pregnant dams, and progesterone decreases or attenuates cocaine-induced behavioral and reward responses. It has been postulated that cocaine's modulation of serum progesterone levels may in turn alter progesterone receptor activity, thereby contributing to cocaine-induced alterations of neuronal functions and genomic regulations. To test this hypothesis, intact male rats received acute injections of saline or cocaine (15 or 30 mg/kg, dissolved in 0.9% saline, intraperitoneal). Progesterone serum levels, progesterone receptor (PR) protein levels, and PR-DNA binding complexes were measured in the striatum by radioimmunoassay, Western blot, and gel shift analyses, respectively. After injection of 15 mg/kg of cocaine, induction of progesterone serum levels was closely followed by an increase in receptor protein levels and DNA binding complexes. After injection of 30 mg/kg of cocaine, similar effects were observed along with an attenuation of receptor protein levels and DNA binding complexes at 60 min. Our results suggest that activation of progesterone receptors may be a mechanism by which cocaine mediates behavior through molecular alterations in the central nervous system.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

The effect of administering a dopamine agonist (Cabergoline) on follicular and luteal development during pro-estrus and estrus in the female greyhound

To study the effect of the dopamine agonist Cabergoline, on ovarian activity in the female dog during pro-estrus and estrus, 6 greyhounds were treated with 5 microg/kg per os of Cabergoline for 20 days beginning on the first day of pro-estrus; 6 animals were left untreated (controls). Ovarian morphology was determined by ultrasound examination once a day during pro-estrus and twice a day during estrus. Follicles were divided into three classes on the basis of their diameter: F1 (<3mm), F2 (3-6mm) and F3 (>6mm). The presence and diameters of post-ovulatory follicles (F-POST) and corpora lutea (CL) were also recorded. Blood samples were taken once a day during pro-estrus and twice a day during estrus. The plasma was assayed for LH, prolactin and progesterone by radioimmunoassay. There were no differences between Cabergoline-treated and control dogs in the duration of pro-estrus or estrus. There was a progressive increase in follicle diameter from the start of pro-estrus when follicles were mainly class F1 to the day of estrus when follicles were mainly class F3. Three days after the start of estrus, the first F-POST follicles were detected. This pattern of development continued and on day 5 the first CLs were detected. By day 9, only CLs were detected. The peak of pre-ovulatory LH was within 3 days of estrus and ovulation was detected in all animals within 3 days of the LH peak. There were no differences in LH concentrations between groups. Plasma prolactin levels varied between animals and were reduced in treated dogs, however, this was not statistically significant (P=0.12). Plasma progesterone levels were below 1.0 ng/ml before the LH surge and thereafter gradually increased. There were no differences in plasma progesterone concentrations between treated and control dogs. In conclusion these results show that the administration of the dopamine agonist Cabergoline during pro-estrus and estrus did not affect the duration of pro-estrus or estrus or the pattern of follicular and luteal development in female dogs.

Dopamine receptors in equine ovarian tissues

Dopamine (DA) agonist and antagonist treatments can affect ovarian reproductive events in the mare. To support our theory that DA produces these effects by acting directly on the ovary, we analyzed equine ovarian tissues for the presence of dopamine receptor-1 (D1r) and dopamine receptor-2 (D2r) mRNA by reverse transcription polymerase chain reaction (RT-PCR) and D1r and D2r proteins by Western blot and immunohistochemistry (IHC). RT-PCR was performed on RNA isolated from ovarian cortex, medulla, granulosa/theca or corpus luteum (CL) tissues and from pituitary (D2r control) and renal artery (D1r control). D1r and D2r specific primers were designed from partial DNA sequences known for the horse (D2r) or conserved sequences from other species (D1r). Western blot analyses were conducted on CL, cortex and granulosa/theca samples and IHC was performed on CL tissues using D1r or D2r specific antibodies. The incidence of positive D2r mRNA was high in CL and ovarian cortex, low in granulosa/theca, and not detectable in ovarian medulla. Dopamine D1r mRNA incidence was high (50%) only in CL tissues. D1r and D2r antibody staining was positive for each tissue type analyzed by Western blot procedures. All CL tissues prepared by IHC showed positive staining for D1r and D2r proteins. Both DA receptor proteins appeared uniformly distributed throughout the CL tissue. These results indicate that equine ovarian tissues do possess D1r and D2r, and suggests that DA can act directly on ovarian tissues through its interaction with DA receptors.

Gonadal hormones provide the biological basis for sex differences in behavioral responses to cocaine

Both clinical and rodent studies show sexually dimorphic patterns in the behavioral response to cocaine in all phases of the addiction process (induction, maintenance, and relapse). Clinical and rodent studies also indicate that hormonal fluctuations during the menstrual/estrous cycle modulate cocaine-induced subjective effects in women and locomotor activity in female rats. Evidence suggests that gonadal hormones underlie these observed differences and could be the biological basis of sex-specific differences in cocaine addiction. To study the effects of gonadal hormones on cocaine-induced activity, two approaches have been used. First, studies have examined the role of endogenous hormones through gonadectomy (GDX) and side-by-side comparisons with intact rats. Second, the individual contributions of testosterone, progesterone, and estrogen have been determined by hormone replacement in GDX rats. In this review, we discuss gonadal hormones as the biological basis for the behavioral responses to cocaine, and the clinical implications of these findings.

In vitro production of progesterone and estradiol by rat granulosa cells regulated by cabergoline and prolactin

Cabergoline (CG), a dopamine agonist, and prolactin (PRL) added in vitro to isolated granulosa cells from immature rats cultured in serum-free medium inhibited FSH-stimulated production of progesterone. The lowest effective concentrations of CG and PRL were 10(-8)M and 1 ng/mL, respectively. In combination, the inhibitory activities were additive. CG at 10(-8) M also suppressed estradiol production by isolated rat granulosa cells; whereas PRL did not. In conclusion, CG inhibits FSH-stimulated progesterone and estradiol production by rat granulosa cells.

Inhibition by amphetamine of testosterone secretion through a mechanism involving an increase of cyclic AMP production in rat testes

1. The effect of amphetamine on the secretion of testosterone and the production of testicular adenosine 3':5'-cyclic monophosphate (cyclic AMP) in rats was studied. 2. A single intravenous injection of amphetamine decreased the basal and human chorionic gonadotropin (hCG)-stimulated levels of plasma testosterone. Plasma LH levels were not altered by the injection of amphetamine. 3. Administration of amphetamine in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone. 4. Amphetamine enhanced the basal and hCG-increased levels of cyclic AMP accumulation in vitro in rat testes. 5. These results suggest that amphetamine inhibits the spontaneous and hCG-stimulated secretion of testosterone from the testes through a mechanism involving an increase in cyclic AMP production.