Effects of dopaminergic and cholinergic interactions on rat behavior.

The present work studied the effects of dopaminergic and muscarinic receptor agonists and antagonists on rat locomotor activity and catalepsy. Results showed that carbachol at the highest dose used (10 mg/kg, p.o.) decreased and pimozide at the dose used abolished locomotor activity. Atropine at a low dose (1 mg/kg, p.o.) increased and at a high dose decreased this parameter. Mazindol at a high dose also increased locomotor activity. A significant and dose-dependent increase in the time on the bar was observed in animals treated with carbachol or pimozide as compared to controls. The increase observed with pimozide was greater than 60 s. Effects of carbachol on locomotor activity were observed already after the first drug exposure, but the increased time on bar produced by this drug in the test of catalepsy was observed only after repeated exposure (7th day). The effect of the highest dose (10 mg/kg, p.o.) of atropine (decreased activity) as related to the lowest one was evident at the 7th day, but the increased locomotor activity seen at the low dose was detected already at the first day. There was a predominance of the effect of pimozide on the open field as well as on catalepsy after its association with each one of the three doses of carbachol. The association of atropine and mazindol did not seem to alter locomotor activity and catalepsy as related to each drug alone. Our results indicate that interactions between dopaminergic and cholinergic systems play an important role on behavior and motor functions.     

Hyperprolactinemia in monkeys: Induction by an estrogen-progesterone synergy

To evaluate the synergistic effect of estrogens and progesterone on prolactin secretion, rhesus and cynomolgus monkeys in the early follicular phase received estradiol benzoate (100 μg/kg/day, sc) alone for 14 days, then in combination with progesterone (subcutaneous silastic capsule) for an additional 14 days. Blood was drawn daily by femoral venipuncture under ketamine hydrochloride anesthesia (15mg/kg). Similarly, this protocol for exogenous steroid treatment was employed in a monkey having a chronically indwelling (femoral insertion into the vena cava) cannula maintained by a vest and mobile tether apparatus; however, no anesthesia was used to obtain serum specimens. In addition, this assembly was applied to six monkeys to determine the acute effects of ketamine hydrochloride on prolactin secretion. Concentrations of prolactin, estradiol-17β, and progesterone in serum were determined by conventional radioimmunoassays. Under estrogen therapy alone, mean circulating prolactin levels declined from ~15 to < 5 ng/ml; in contrast, the addition of progesterone caused an abrupt serum prolactin elevation, ~8–12 fold. This estradiol-progesterone course led to sustained hyperprolactinemia in the chronically catheterized Monkey, whereas ketamine administration raised serum prolactin only briefly, the elevation lasting less than three hours after injection. These findings establish that an estrogen-progesterone synergy, separate from the transient effects of ketamine, Induced hyperprolactinemia in cycling monkeys having prevailing levels of estrogen and progesterone near those characteristic of late gestation, when sustained prolactin elevations are observed normally.     

Metachlopromide-induced hyperprolactinemia fails to affect ovarian cyclicity in the common marmosets (Callithrix jacchus)

Intramuscular administration of metachlopromide (2.5, 5, and 10 mg) induced a dose-dependent increase in plasma prolactin levels. The magnitude and duration of metachlopromide-induced hyperprolactinemia were also dose related. However, metachlopromide treatment (5 mg/day) for 60 days failed to affect ovarian function in the common marmoset as evidenced by ovulatory plasma estradiol and progesterone profiles. During the pretreatment cycle, there was no consistent pattern in plasma prolactin levels depending on the stage of cycle. During lactation, higher levels of plasma prolactin were observed.     

Ovarian responses to perphenazine-induced prolactin secretion in the rats: Effect of ovulation, stress, and steroids.

A single injection of 2.5 mg perphenazine (PH)/kg body wt to rats on the day of estrus (day 0) did not result in increased serum progesterone 24 hr later. Continued daily injections, however, resulted in a 2.5-fold increase in serum progesterone between days 1 and 3 and a 1.6-fold increase between days 3 and 5 to a final concentration of 58 plus or minus 4 ng/ml on day 5 in serially anesthetized and bled rats. Neither daily administration of 5.0 nor 10.0 mg PH/kg body wt to rats subjected to the stressful conditions of this regimen resulted in further increases in serum progesterone, but the 5.0 mg dose of PH in unstressed rats bled only on day 5 resulted in a highly significant increase in serum progesterone to 110 plus or minus 7 ng/ml. In unstressed rats the increase in serum progesterone over control values after five daily injections of 2.5 mg PH/kg body wt could be attributed to decreased 20alpha-reduction of progesterone, but when the dose of PH was increased to 5.0 mg/kg, a highly significant increase in both progesterone and total progestins occurred indicating that prolactin can increase steroidogenesis as well as reduce 20alpha-hydroxysteroid dehydrogenase activity. After inhibition of ovulation, the 5.0 mg daily dose of PH resulted in serum progesterone of only 25 plus or minus 8 ng/ml on day 5 in unstressed rats. Thus, serum progesterone in ovulating rats treated with PH originated primarily in the corpora lutea. Perphenazine, 5.0 mg/kg, administered only on estrus and the first day of diestrus was sufficient to induce pseudopregnancy of 14.5 plus or minus 1.6 days. No evidence for gonadotropin stimulation of the ovaries of any rats was observed. The effect of stress on the progesterone response was not mimicked by administration of cortisol acetate and is assumed to be medicated by suppression of prolactin secretion.     

Effect of serotonin depletion by p-chlorophenylalanine on serum prolactin levels in estrogen-treated ovariectomized rats: insights concerning the serotoninergic, dopaminergic and opioid systems.

The stimulatory effect of serotonin on prolactin secretion is well documented, and the administration of an inhibitor of serotonin synthesis (p-chlorophenylalanine - pCPA) has the expected inhibitory action on prolactin release in most experimental situations. However, there is evidence that in certain physiological or experimental conditions, activation of the serotoninergic system can also determine inhibition of prolactin secretion. The aim of the present study was to investigate the ability of estrogen to modify the effect of pCPA on prolactin secretion and to evaluate the participation of opioid and/or dopaminergic systems in regulating pCPA-induced prolactin secretion in estradiol-treated rats. We observed that pCPA administration (200 mg/kg/day, s.c., 2 days) to ovariectomized (OVX) female rats treated with estradiol benzoate (300 microg/week for 2 weeks, or 50 microg/week for 4 weeks, s.c.) causes a significant increase in serum prolactin, whereas no effect is observed in intact rats or in OVX rats without treatment. Bromocriptine administration completely reversed prolactin values previously increased by estradiol and by pCPA [OVX rats + estradiol = 86.50 ng/ml (68.90-175.02), OVX + estradiol + pCPA = 211.30 ng/ml (142.03-311.00), OVX + estradiol + pCPA + bromocriptine = 29.35 ng/ml (23.01 - 48.74), p<0.05. Naloxone administration partially reduced estrogen-induced high prolactin concentrations, but did not affect prolactin secretion stimulation determined by pCPA. Overall, the data from this report confirm the involvement of the dopaminergic system and, to a lesser degree, of endogenous opioids in prolactin secretion stimulation determined by estradiol. Furthermore, our results suggest that the stimulatory action of pCPA on prolactin secretion in estradiol-treated OVX rats is mediated by serotonin, which may also act indirectly on dopamine neurons.     

Diurnal Variations of Striatal D2 Dopaminergic Receptors and its Relation with Haloperidol-induced Catalepsy

In spite of the clear evidences for the blockade of dopaminergic D2 receptors as the mechanism of action for haloperidol-induced catalepsy, the contribution of pharmacokinetic and pharmacodynamic aspects on the diurnal modulation of haloperidol-induced catalepsy is controversial. We studied the diurnal variations of striatal dopamine receptors and its relation with catalepsy diurnal variations. The [ 3 H]-spiperone binding to dopamine receptors had a clear rhythm with a peak at 00:00 to 03:00 h, and a trough at 12:00 to 18:00 h. Haloperidol-produced catalepsy measured with the four-cork test, also showed a clear rhythm, with a peak at 00:00 h and trough at 9:00 h. The dose-response curves at peak and trough of catalepsy had the same ED 50 (0.12 mg), with time-related changes in the maximal effect. Similar diurnal variations between catalepsy and dopamine receptor binding, indicate a relevant role of temporal pharmacodynamics of haloperidol on the modulation of its behavioral effects.     

Modulatory effects of PLG and its peptidomimetics on haloperidol-induced catalepsy in rats.

A behavioral model of dopaminergic function in the rat was used to examine the anticataleptic effects of L-prolyl-L-leucyl-glycinamide (PLG) and peptidomimetic analogs of PLG. Administration of 1 mg/kg PLG intraperitoneally significantly attenuated haloperidol (1 mg/kg)-induced catalepsy (as measured by the standard horizontal bar test), whereas doses of 0.1 and 10 mg/kg PLG did not. Eight synthetic PLG peptidomimetics (Calpha, alpha-dialkylated glycyl residues with lactam bridge constraint [1-4] and without [5-8]) were tested in the same manner (at a dose of 1 microg/kg) and categorized according to their activity, i.e. very active (5), moderately active (2, 3, 4, and 6), and inactive (1, 7, and 8). The catalepsy-reversal action of the diethylglycine-substituted peptidomimetic 5 was examined further and found to exhibit a U-shaped dose-response effect with an optimal dose of 1 microg/kg. The similarity between the effects of PLG and the synthetic peptidomimetics suggests a common mechanism of action. Finally, the synthetic peptidomimetics examined here, particularly peptidomimetic 5, were more effective than PLG in attenuating haloperidol-induced catalepsy.     

Diurnal Variations of Striatal D2 Dopaminergic Receptors and its Relation with Haloperidol-induced Catalepsy

In spite of the clear evidences for the blockade of dopaminergic D2 receptors as the mechanism of action for haloperidol-induced catalepsy, the contribution of pharmacokinetic and pharmacodynamic aspects on the diurnal modulation of haloperidol-induced catalepsy is controversial. We studied the diurnal variations of striatal dopamine receptors and its relation with catalepsy diurnal variations. The [3 H]-spiperone binding to dopamine receptors had a clear rhythm with a peak at 00:00 to 03:00 h, and a trough at 12:00 to 18:00 h. Haloperidol-produced catalepsy measured with the four-cork test, also showed a clear rhythm, with a peak at 00:00 h and trough at 9:00 h. The dose-response curves at peak and trough of catalepsy had the same ED 50 (0.12 mg), with time-related changes in the maximal effect. Similar diurnal variations between catalepsy and dopamine receptor binding, indicate a relevant role of temporal pharmacodynamics of haloperidol on the modulation of its behavioral effects.     

The effect of frontal cortex lesion on the activity of the dopaminergic system in rat striatum

The experiment was carried out on male Wistar rats weighing 180-220 g with lesion in the cortex of the frontal lobe. The activity of the dopaminergic system was studied by means of behavioural tests such as determination of spontaneous motor activity, apomorphine-induced stereotypy, haloperidol-induced catalepsy. Increased intensity of stereotypy was observed reaching a maximum 14 days after frontal lobe damage. Moreover, a slight tendency was observed for inhibition of haloperidol-induced catalepsy without changes in the spontaneous motor activity of the animals. Biochemical investigations demonstrated reduced dopamine content in the striatum on the side of the lesion.     

The effect of calcitonin on prolactin secretion during gestation

The relationship between calcitonin (CT) and prolactin (PRL) was studied by means of the injection of salmon calcitonin (SCT) i.p. on day 1 of gestation. An estrogen inhibitor - clomiphene - was also administered to certain groups of animals on day 4 and 5 of gestation. SCT did not affect PRL levels on day 1 of gestation nor on days 5 or 7, but it prevented the rise of PRL levels observed in animals submitted to injection stress on days 4 and 5. In animals treated with clomiphene, the inhibition by SCT on PRL increase after injection stress was partially abolished. SCT while not affecting basal PRL level prevented the rise observed after stress and this effect occurred some days later. Thus SCT could exercise a delayed neuroendocrine control. This action of SCT seemed to be partially dependent upon the presence of estrogens.     

Synthesis of 61-bis(1-adamantylcarbamoyl)-1,2-methano[60]fullerene and its antagonistic effect on haloperidol-induced catalepsy in mice

The 61-bis(1-adamantylcarbamoyl)-1,2-methano[60]fullerene was synthesized from N,N'-di(1-adamantyl)malondiamide and C(60) in the presence of 1,8-diazabicyclo[5,4,0]-7-undecene. The intraperitoneal administration of this fullerene derivative (10mg/kg) caused an antagonistic effect on haloperidol-induced catalepsy in mice.     

Indomethacin fails to alter basal or phenothiazine-induced prolactin concentrations in man.

In order to evaluate the possible role of prostaglandins in pituitary prolactin (PRL) secretion, PRL was serially measured following perphenazine (Trilafon) ingestion in 8 men before and after 5 days of indomethacin administration. Since estrogens have been shown to modulate prolactin secretion in man, serum steroids including estrone (E1), estradiol (E2), progesterone (P) and testosterone (T) were measured before and after indomethacin ingestion. Serum E1, P and T levels were similar during the pre- and post-indomethacin study periods: 56 +/- 4 (1 SEM) vs 48 +/- 5 pg/ml, 298 +/- 28 vs 315 +/- 32 pg/ml, and 8.1 +/- 0.7 vs 8.6 +/- 0.7 ng/ml, respectively. Serum E2 levels were slightly, but significantly, lower following indomethacin treatment at 30 +/- 3 vs 37 +/- 3 pg/ml (p less than .01). Basal serum PRL concentrations were unaffected by indomethacin administration (9 +/- 3 pre- vs 8 +/- 2 ng/ml post-drug treatment). Integrated perphenazine-induced PRL responses were likewise similar during the 2 study periods: 101 +/- 16 ng . hr/ml during the control period and 104 +/- 14 ng . hr/ml following indomethacin. Thus, short-term indomethacin treatment had no effect on basal or perphenazine-stimulated PRL secretion in men.     

Evidence that serotonin neurons stimulate secretion of prolaction releasing factor.

The purpose of the present study was to determine if serotonin was stimulatory to prolactin release by inhibition of the dopaminergic system or by stimulating release of a prolactin releasing factor (PRF). We measured the amount of prolactin secreted after administration of 30 mg/kg of 5-hydroxytryptophan (5-HTP) to male rats pretreated with fluoxetine (10 mg/kg) and compared it with the amount of prolactin released in male rats treated with αmethyl-p-tyrosine methyl ester (αMT) or various dopamine receptor blocking agents. In every experiment the serotonergic stimulus provided by 5-HTP in fluoxetine-pretreated rats released considerably more prolactin than did treatment with αMT or dopaminergic blockers. We conclude that serotonin releases prolactin not by inhibiting dopaminergic neurons but rather by stimulating the release of PRF.     

Catalepsy induced by morphine or haloperidol: effects of apomorphine and anticholinergic drugs.

To investigate the extent of cholinergic involvement in opiate-induced catalepsy, the effects of three anticholinergic drugs were studied on morphine-induced catalepsy. Haloperidol-induced catalepsy was also examined. Maximum catalepsy in rats was obtained with 30 mg/kg morphine or 3 mg/kg haloperidol. The anticholinergic drugs atropine, benztropine, and scopolamine were unable to antagonize morphine-induced catalepsy, yet readily antagonized haloperidol-induced catalepsy. Low doses of apomorphine (7.5 mg/kg), on the other hand, readily antagonized morphine catalepsy, but 13-fold higher doses of apomorphine were needed to block haloperidol-induced catalepsy. The results are compatible with the idea that catalepsy can be mediated via the striatum or the amygdala; morphine-dopamine antagonism may occur in the amygdala, whereas morphine-dopamine-cholinergic interactions occur in the striatum.     

Role of N-methyl-D-aspartate (NMDA) receptors in experimental catalepsy in rats

N-methyl-D-aspartic acid (NMDA; 40 mg/kg, i.p.) did not elicit catalepsy, but it potentiated the cataleptic effect of haloperidol and GABAB receptor agonist, baclofen. MK-801 (0.2 mg/kg, i.p.), NMDA-receptor antagonist, reversed haloperidol- but not baclofen-induced catalepsy. MK-801 also potentiated the anticataleptic effect of scopolamine and bromocriptine against haloperidol-induced catalepsy. Dihydropyridine (DHP) calcium-channel antagonists such as nimodipine and nitrendipine (10 mg/kg, i.p.), reversed the anticataleptic effect of MK-801, and potentiated the cataleptic effect of haloperidol, as well as baclofen. These observations indicate the involvement of NMDA receptors in catalepsy, and suggest a potential clinical implication of NMDA-receptor antagonists in Parkinson's disease.     

Evidence for dopaminergic regulation of prolactin and a luteotropic complex in the ferret

The role of dopaminergic agents in prolactin (Prl) release and the luteotrophic role of Prl and luteinizing hormone (LH) were investigated in pseudopregnant female ferrets. A single injection of the dopamine antagonist pimozide (0.63 mg/kg) resulted in a tenfold elevation of plasma Prl in anestrous females. Subcutaneous injection of pimozide on alternate days from Day 2 through Day 16 of pseudopregnancy elevated both Prl and progesterone levels. Daily treatment with the dopamine agonist 2 alpha-bromoergocryptine (bromocriptine, 4 mg/kg), from Day 2 through Day 16 of pseudopregnancy lowered levels of both plasma Prl and progesterone. Neither pimozide nor bromocriptine had a direct effect on progesterone secretion by luteal cells in vitro. Daily intraperitoneal administration of a monoclonal antibody against gonadotropin-releasing hormone from Day 2 through Day 10 of pseudopregnancy lowered both plasma LH and progesterone, but had no effect on plasma Prl concentrations. Daily administration of equine antisera against bovine LH or 100 IU of human chorionic gonadotrophin to pseudopregnant ferrets lowered progesterone levels. It is concluded that Prl release is influenced by dopaminergic compounds, and both Prl and LH are required for luteal maintenance in the ferret.     

Effects of pimozide and domperidone administration on prolactin levels in neonatally estrogenized female rats

The effects of two dopaminergic blockers, pimozide and domperidone, on the prolactin secretion were investigated in adult female rats treated neonatally with estrogens (100 micrograms of estradiol benzoate s.c. on day 1). These rats showed hyperprolactinemia (556 micrograms/l vs 57.7 in oil-injected) and treatment with pimozide or domperidone failed to increase prolactin levels in the adult age. These results suggest that the hyperprolactinemia in neonatally estrogenized female rats is produced by loss of the dopaminergic inhibition on prolactin secretion, so that the pharmacological blockade of dopaminergic receptors is uneffective. The dopamine levels in hypothalamus were similar in control and estrogenized females suggesting that failure in dopaminergic inhibition is due to a decrease in dopamine secretion to portal vessels.     

Dual action on central dopamine function of transdihydrolisuride,a 9, 10-dihydrogenated analogue of the ergot dopamine agonist lisuride

Transdihydrolisuride (TDHL), a 9, 10-dihydrogenated analogue of the ergot dopamine (DA) agonist lisuride (LIS), was investigated for its influence on central dopaminergic functions in rats and mice after single i.p. administration. TDHL (0.39–25 mg/kg) unexpectedly induced catalepsy and antagonized apomorphine-induced stereotypes in rats; it was approx. 3–5 times less potent than the DA antagonist haloperidol. TDHL (0.025–6.25 mg/kg) caused hypokinesia and antagonized the apomorphine-induced hyperactivity in rats. Pre-treatment with TDHL (0.78–12.5 mg/kg) which per se did not alter thermoregulation at room temperature, antagonized the hypothermia induced by the DA agonist apomorphine (5 mg/kg i.p.) in mice. These DA antagonistic properties contrasted with the prolactin (PRL) lowering effect of TDHL (0.01–10 mg/kg p.o.) in reserpinized female rats thus indicating DA agonist function. PRL inhibition tended to be longer lasting (>8h) than after LIS (0.01–1 mg/kg p.o.) with comparable potency. In healthy volunteers TDHL (0.2–1 mg p.o.) effectively lowered PRL levels with similar potency but with a markedly longer duration of action than LIS (>24h after 0.5 mg TDHL). In contrast to the side effects after acute LIS treatment, no comparable adverse reactions such as nausea, emesis or postural hypotension typical for DA agonists could be observed with effective PRL lowering doses of TDHL. The unique profile of TDHL on DA functions suggests its usefulness as a potent, longlasting PRL inhibitor with less unwanted effects. The behavioural findings indicate the potential usefulness of TDHL as a neuroleptic, which due to its partial DA agonistic action, should lack typical extrapyramidal or neuroendocrine side effects of classic DA receptor blocking agents. Possible implications of the dual function of TDHL upon central DA receptors are discussed with regard to the incidence of side effects or selectivity of action for other conceivable therapeutic indications.     

Clinical, biological and hormonal study of mid-pregnancy termination in cats with aglepristone

In order to evaluate the efficacy, the safety and the variation in plasma concentrations of estrogens, progesterone, PGFM, oxytocin, cortisol and prolactin after mid-pregnancy termination induced by aglepristone, 61 pregnant queens (33.3 + 4.2 days), were injected subcutaneously with 15 [corrected] mg/kg aglepristone, (Alizine) [corrected] repeated once 24 h later. Five queens served as control and received a placebo. The efficacy of aglepristone was 88.5% and termination of pregnancy was achieved in 50% of the queens within 3 days. Brief periods of depression and anorexia were noted in 9.3% of the queens before fetal expulsion (these symptoms were attributed to the phenomenon of fetal expulsions). Not one of the queens that aborted developed uterine disease. There were no changes in plasma concentrations of estrogen, prostaglandin, prolactin or oxytocin following aglepristone administration. However, there were significant increases in plasma concentrations of progesterone and cortisol 60 and 30 h, respectively, after aglepristone administration. Termination of pregnancy occurred with high plasma progesterone concentrations. Fetal expulsion was characterised by an increase in estrogen, PGFM and oxytocin concentrations, whereas prolactin and cortisol levels remained at a basal level.     

Lipoprotein augmentation of human chorionic gonadotropin and prolactin stimulated progesterone synthesis by rat luteal cells

A collagenase dispersed cell suspension from PMSG-hCG primed immature rats responded to exogenously added hCG, cholera enteroxin, prolactin, and 8-Bromocyclic-AMP with increase in progesterone production in a dose dependent manner, and this stimulation was augmented by the plasma lipoprotein fractions hHDL and hLDL. The responsiveness to low doses of prolactin was not apparent when lipoprotein fractions were not included in the assay mixture. When the incubation mixture contained either LDL or HDL, the stimulatory effect of prolactin on progesterone production was evident at 5 and 10 micrograms prolactin/ml of the incubation mixture. Progesterone production, both basal and hormone stimulated, was maximum on day 7 of pseudopregnancy. Although the extent of hCG and prolactin stimulation of progesterone production and its potentiation by lipoprotein fractions was observed to be higher on days 3 and 5 than that seen on day 7, the net amount of progesterone produced was highest on day 7. The basal as well as hormone and lipoprotein stimulated progesterone production started to decline after day 7, reaching a nadir on day 14. These experiments show that prolactin is effective in stimulating progesterone production by rat luteal cells in vitro and that lipoprotein fractions, LDL and HDL further potentiate this response. This study further suggests that it is important to include LDL or HDL as a source of cholesterol for in vitro experiments in which the steroidogenic response of luteal cells to exogenous stimuli is tested.