Circling behaviour in rats with unilateral lesions of the nigrostriatum induced by 6-hydroxydopamine: changes induced by oral administration of cytidine-5'-diphosphocholine.

A unilateral administration of 6-hydroxydopamine into the nigrostriatal system of the rat was responsible for ipsiversive circling behaviour in response to administration and, in time, of contraversive circling behaviour in response to L-DOPA and apomorphine. This contraversive circling behaviour appears to be mediated by the development, on the lesioned side, of supersensitivity of postsynaptic dopamine receptors. Subchronic treatment with cytidine-5'-diphosphocholine (p.o.) by itself was devoid of behavioural effects. The CDP-choline did not modify the apomorphine-induced stimulant effect but potentiated the circling behaviour produced by L-DOPA and amphetamine. The data show that the effects of CDP-choline were mediated by a presynaptic mechanism: the potentiation of the effects of L-DOPA cannot be explained by an activation of tyrosine hydroxylase, but seems to be related to an improvement of release of newly synthesized dopamine from exogenous L-DOPA.

Differential regulation of tyrosine hydroxylase and estradiol receptor expression in the rainbow trout brain.

In numerous fish species, dopamine has been found to strongly inhibit gonadotropin release. Among the enzymes that regulate dopamine turnover, tyrosine hydroxylase (TH), the rate-limiting anabolic enzyme, could be a target for endocrine feedback regulation. Since dopamine turnover is stimulated by estradiol in rainbow trout, we have investigated the effect of estradiol on TH and estradiol receptor expression. In situ hybridization was used to quantify mRNA levels in the brain of ovariectomized female rainbow trout implanted or not with estradiol pellets. We demonstrated that preoptic TH and estradiol receptor mRNA levels are greatly decreased by gonadectomy during vitellogenesis. For TH expression, this effect was reversed in part by estradiol supplementation. We have also confirmed the existence of an inhibitory gonadal feedback on FSH secretion, mediated by estradiol. The stimulating effect of estradiol on TH expression found in this study could be a pathway involved in gonadal feedback on gonadotropin release.

Absence of direct regulation of prolactin cells by estradiol-17 beta in rainbow trout (Oncorhynchus mykiss).

The effects of estradiol-17 beta (E2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout (Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17 beta did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17 beta effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17 beta and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of pituitary dopamine D1 or D2 receptors and secretion of follicle stimulating hormone and luteinizing hormone during the annual reproductive cycle of female rainbow trout.

The two gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) have distinct temporal expression and release profiles in fish, but little is known regarding their neuroendocrine control, especially for FSH. The present experiments were performed on previtellogenic, mature and preovulatory female trout. The catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine, increased plasma LH and FSH concentrations of mature fish. The dopamine agonist apomorphine decreased and the dopamine antagonist domperidone increased plasma LH concentration of preovulatory fish and delayed ovulation, but did not modify plasma FSH concentration. The dopamine D2 agonist bromocryptine inhibited LH release in cultured gonadotrophs from mature and preovulatory fish, but not from previtellogenic fish. Bromocryptine also significantly inhibited basal and salmon gonadotrophin releasing-hormone (sGnRH)-induced FSH release from cultured gonadotrophs of mature fish, but not of preovulatory fish, and increased FSH release from gonadotrophs of previtellogenic fish. The dopamine D1 agonist SKF 38393 had no observed effect on the release of FSH and LH, at any reproductive stage studied. The D1 agonist SKF 38393, the D2 agonist bromocriptine and sGnRH had no observed effects on cell contents of FSH and LH. Taken together, these data suggest that, at the level of the pituitary, dopamine inhibits LH release as vitellogenesis proceeds, via activation of dopamine D2 receptors. We demonstrate for the first time in fish a control of FSH release (a dopamine control), especially in mature fish which have low circulating concentrations of FSH.

Influence of oxygen availability on the neurotoxic effect of 6-hydroxydopamine on nigro-striatal dopaminergic neurons.

The neurotoxin 6-hydroxydopamine (6-OHDA) was intracerebroventricularly injected (50 micrograms per mouse) in mice submitted to various oxygenation conditions and the striatal levels of dopamine (DA) and its metabolites were determined by HPLC 7 days later. In normoxic conditions the striatal depletion in DA reached 50%. This effect was not modified by a normobaric hypoxia (10% O2) applied 30 min before and 30 min after the 6-OHDA injection. On the contrary, the neurotoxic effect was reduced when the hypoxia was prolonged up to 11 h after the drug administration. When a normobaric hyperoxia (60% O2) was applied 30 min before and 11 h after the 6-OHDA injection, the neurotoxic effects of the latter were not modified. These data, as well as other results obtained from ex vivo experiments showing that normobaric hypoxia or hyperoxia did not modify the striatal synaptosomal [3H]DA uptake, indicate that oxygen availability does not exert a critical influence on the efficiency of the neuronal dopamine uptake complex.

Alcohol and GABA: ethanol intake modifies hippocampal nipecotic acid binding in ethanol-preferring and non-preferring rats.

3H-nipecotic acid (3H-NIP) binding to GABA uptake recognition sites was studied in the hippocampus of 3 groups of male, Long Evans rats: Group 1: ethanol-naive rats (ENR); Group II: ethanol-preferring rats (DR) and non-preferring rats (NDR), which had consumed about 5 g.kg-1.d-1 and 1 g-1.d-1 of alcohol respectively in the form of a 12% ethanol solution prior to 3H-NIP binding analysis; Group III: DR and NDR who had had no access to ethanol for 21 d after the initial exposure of ethanol solution (28 d). Binding studies showed that ethanol drunk by both DR and NDR in Group II decreased 3H-NIP binding (Bmax decreased) with an enhancement of affinity (KD decreased). In rats subjected to withdrawal of ethanol (Group III), affinity of 3H-NIP for GABA uptake sites was higher than in controls (Group I), but lower than in Group II, Bmax in this group being higher than in the 2 other groups. In Group III, KD was higher in DR than in NDR. These results showed that ethanol intake, in a free-choice paradigm, altered 3H-NIP binding, and that differences in ethanol intake between DR and NDR were associated with differences in sensitivity of hippocampal GABA uptake sites. These differences in 3H-NIP binding could either precede ethanol intake, or be a direct result from it. The results, together with data from other laboratories suggest that: 1), 3H-NIP binding sites are involved in the regulation of ethanol intake; 2), 1 factor responsible for individual differences in ethanol response is reflected by the GABA uptake system.

A homotaurine derivative reduces the voluntary intake of ethanol by rats: are cerebral GABA receptors involved?

The effects of some derivatives of homotaurine (3 APS), the well known GABA agonist, were tested on the voluntary intake of ethanol by rats. Spontaneously ethanol drinking rats (DR) were selected and had a constant voluntary intake of ethanol by rats. Spontaneously ethanol drinking rats (DR) were selected and had a constant voluntary intake of a 12% ethanol solution (VIE) during 14 days (about 5 g/kg body weight daily). Calcium acetylhomotaurine (0.26 and 0.52 mmol/kg daily IP) significantly reduced VIE and this was inhibited by the GABA antagonist bicuculline (2 mg/kg IP). The conditioned aversion test to saccharin was negative. Bicuculline alone did not affect VIE. Other homotaurine (3-APS) derivatives: sodium acetyl homotaurine (Na AOTA), homotaurine (OTA), sodium acetyltaurine (Na A TA) and calcium chloride (CaCl2) did not affect VIE. These data suggest that the gabaergic system could be implicated in VIE. MERAM Lab. patent.

Isolation and striatal (3H) serotonin uptake: role in the voluntary intake of ethanol by rats.

Ethanol preferring rats were selected and showed a constant voluntary intake of a 12 percent ethanol solution during 14 days (about 5 g/kg body weight daily). Analysis of 3H serotonin uptake by striatal synaptosomes showed that steady state 3H serotonin synaptosomal levels were lower in alcohol preferring rats. Grouping these rats (5 per cage) reduced both voluntary intake of ethanol and synaptosomal 3H serotonin uptake. Furthermore, blocking the serotonin uptake by clomipramine 5 mg X kg-1 or 10 mg X kg-1 also reduces voluntary intake of ethanol. These data are in agreement with the hypothesis of a modulation of the voluntary intake of ethanol both by chemical and housing stimulation of striatal receptors for serotonin.

Attenuation by antidepressant drugs of alcohol intake in rats.

Ethanol preferring rats were selected and showed a constant voluntary intake of a 12% ethanol solution during 14 days (about 5 g/kg body weight daily). These alcohol preferring rats were daily IP injected during two weeks with different antidepressant drugs, according to their specificity of action: nomifensine (5 and 10 mg/kg) and maprotiline (2.5 and 5 mg/kg) (dopamine uptake inhibitors), desipramine and metapramine (5 and 10 mg/kg) (noradrenaline uptake inhibitors) clomipramine and doxepin (5 and 10 mg/kg) (serotonin uptake inhibitors). Only desipramine, 5 and 10 mg/kg, metapramine, 10 mg/kg, clomipramine, 5 and 10 mg/kg and doxepin, 10 mg/kg, were able to reduce significantly the ethanol intake. These drugs specifically inhibit noradrenaline or serotonin uptake. These data lead us to think that norepinephrine and/or serotonin, but not dopamine, are involved in the voluntary intake of alcohol.

GABA transmission, but not benzodiazepine receptor stimulation, modulates ethanol intake by rats.

Adult male Long Evans were selected as ethanol preferring rats (DR) during 28 days. After this period, they were daily IP injected during 14 days with one of the next drugs: diazepam 1 mg.kg-1, alprazolam 1 mg.kg-1 (benzodiazepines), progabide 25 mg. kg-1 (GABA A and B agonist), nipecotic acid 150 mg.kg-1 (GABA uptake inhibitor), muscimol 0.2 mg.kg-1 (GABA A agonist), AOAA 10 mg.kg-1 (GABA decarboxylase inhibitor), baclofen 3 mg.kg-1 (GABA B agonist), or NaCl 0.9% (1 ml/200 g). During treatment, rats were isolated, had free access to food, and free choice between ethanol (12%) and water whose respective consumption were daily noted. Among treatments, only AOAA and baclofen were able to decrease significantly ethanol intake, without modifying total liquid intake. The action of these different drugs on GABA transmission and on ethanol intake was discussed. It was concluded that GABA A and benzodiazepine receptors were not implicated in ethanol intake, but that modulation of voluntary ethanol intake could be associated with a modification of GABA metabolism and/or stimulation of GABA B receptors. An intervention of GABA B receptors on noradrenergic pathways was also evoked.

Striatal dopamine does not appear involved in the voluntary intake of ethanol by rats.

Ethanol preferring and non preferring rats were selected. Ethanol preferring rats showed a constant voluntary intake of a 12% ethanol solution during 14 days (about 5 g/kg body weight daily) while the non preferring rats drank less than 1 g/kg body weight daily. Preferring rats were daily IP injected with 5 or 10 mg/kg of nomifensine, an inhibitor of dopamine uptake. Their intake of ethanol solution remained constant during the 14 days of treatment. Dopamine uptake into striatal synaptosomes was identical in ethanol preferring and non preferring rats. These data, as others, led us to suppose that striatal dopamine is not involved in the voluntary intake of ethanol by rats.

Interactive effects of dietary levels of tryptophan and protein on voluntary feed intake and growth performance in pigs, in relation to plasma free amino acids and hypothalamic serotonin.

The effects of dietary level of tryptophan (TRP) and CP content and composition on voluntary feed intake, growth performance, and carcass characteristics in finishing pigs were studied in two experiments, with an equal number of females and castrated males. In Exp. 1, involving 120 Large White pigs from 44 to 99 kg BW with ad libitum access to feed, six treatments were compared according to a 2 x 3 factorial arrangement: 1) two levels of TRP (.09 and .13%), suboptimal and optimal for growth, respectively, 2) three types of CP supply (a 12.5% CP diet based on corn-soybean meal, and adequately balanced for essential amino acids [EAA] other than TRP; 15.7% CP diet with additional protein from corn gluten meal; 16.2% CP diet with additional nonessential amino acids [NEAA, in the form of L-glutamic acid.HCl and glycine], and the same levels of EAA as in the 12.5% CP diet. In Exp. 2, including four of the six previous factorial combinations (.09 and .13% TRP, 12.3 and 15.8% CP with additional protein), 32 pigs of 50-kg initial BW were used during 21 d, and further observations on meat quality characteristics, plasma free amino acid levels, and serotonin concentrations in the posterior hypothalamus were made. The major observed effects were interactions of different magnitude according to sex between TRP level and the amount and the composition of additional CP. At the suboptimal level of .09% TRP, the increase in protein content severely decreased daily feed intake and growth compared with the .13% level, especially in females. Conversely, the addition of NEAA at both TRP levels had little effect on daily feed intake and growth. Deficiency of TRP exerted a significant increase of pH in adductor femoris and semimembranosus muscles measured 45 min and 24 h postmortem, but only in females. Voluntary feed intake, as affected by dietary TRP and CP levels, was linearly related with concomitant changes in TRP to large neutral amino acids (TRP:LNAA) ratio both in feed and in plasma, which in turn was directly associated to hypothalamic serotonin concentration. It was concluded that an overly low concentration of serotonin in the hypothalamus, especially in females, as a result of TRP:LNAA imbalance, could be involved in the reduction of voluntary feed intake.

Circling in normoxic or hypoxic rats with unilateral 6-OHDA nigrostriatal lesion. Part 2. Effects of d-amphetamine.

Unilateral administration of 6-hydroxydopamine into the rat nigrostriatal system induces a unilateral damage of the dopamine (DA) containing neurons. In such lesioned animals, d-amphetamine (AMPH) induces circling behavior (ipsiversive circling) in relation to its DA releasing property in the non-lesioned side. A preexposition to hypoxia potentiates the behavioral effect of AMPH: this can be related to an increase in the amount of substrate available for release, dopamine. Hypoxia occurring just after the administration of AMPH does not initially modify the AMPH induced circling behavior. This suggests that tyrosine hydroxylase inhibition by hypoxia is not a limiting factor of the releasing effect of AMPH. After 20 min of hypoxia, circling decreases. This impairment could be mediated by a decrease of the amount of available DA and/or by a decrease of release.

Circling behavior in normoxic or hypoxic rats with unilateral 6-OHDA nigrostriatal lesion. Part 1. Effects of apomorphine and L-dopa.

Unilateral administration of 6-hydroxydopamine (6-OHDA) into the rat nigrostriatal system provokes circling behavior in response to apomorphine and L-dopa. This behavior appears to be mediated by the development in the lesioned side of a postsynaptic dopamine receptors supersensitivity. Acute hypobaric hypoxia does not modify the apomorphine-induced stimulant effects, but does oppose the L-dopa-induced circling behavior. Our data suggest that effects of hypoxia are mediated by a presynaptic mechanism. The antagonism of the effects of L-dopa cannot be explained by the inhibition of activity of the oxygen-dependent enzyme tyrosine hydroxylase, but seems to be related to an impairment of the release of newly synthesized dopamine from exogenous L-dopa.

Dynamic characteristics of dopamine, norepinephrine and serotonin metabolism in axonal endings of the rat hypothalamus and striatum during hypoxia: a study using HPLC with electrochemical detection.

The metabolism of dopamine, norepinephrine and serotonin was studied in normoxic or hypobaric hypoxic rats, using HPLC with electrochemical detection. The changes in serotonin and its metabolite 5 hydroxy indolacetic acid (5 HIAA) levels in the hypoxic striatum and hypothalamus suggest an inhibition of 5 HIAA formation and a complex interaction between synthesis, release and uptake. Hypoxia caused a decrease of the striatal levels of homovanillic acid (HVA), dihydroxy 3-4 phenylacetic acid (DOPAC) [inhibition of tyrosine hydroxylase (TH) and monoamine oxidase (MAO)] and 3-methoxytyramine (3 MT) (inhibition of release). Striatal dopamine levels were increased, suggesting an increase in granular dopamine storage, with an impaired release. Hypothalamic levels of norepinephrine were decreased during hypoxia [(inhibition of TH, MAO, and dopamine beta-hydroxylase (DBH)].

Survival time in hypoxic mice: differentiation between apomorphine-induced hypothermia and antihypoxic properties.

The effects of apomorphine on survival time of mice during lethal anoxic hypoxia were studied. Apomorphine induced hypothermia and an increase in survival time. Both these effects were mediated by cerebral dopamine receptors, however with different affinity for the neuroleptics haloperidol and sulpiride. These data suggest that apomorphine's antihypoxic effect is not only mediated by the classical effect of hypothermia but also by slowing of oxydative metabolism.

Potentiation by an alpha-adrenolytic agent, nicergoline, of the cardiac effects of propranolol.

Ten young healthy volunteers were given placebo, propranolol (20 or 40 mg), nicergoline, an alpha blocking agent (30 mg) or the association of nicergoline (15 mg) and propranolol (20 mg) in a randomized double blind study. The results show that nicergoline potentiates the cardiodepressant action of propranolol, whereby the effects of 20 mg become the same as those of 40 mg given alone on cardiac output and myocardial oxygen demand, though the plasma propranolol levels are not changed. We, therefore, propose that nicergoline blocks alpha 1 agonist effects of propranolol, which are usually masked by the greater beta 1 blocking effects but could have clinical and therapeutic relevance.

Oxotremorine-induced cholinergic syndrome: modifications by levodopa and/or oral cytidine diphosphocholine.

A peripheral and cerebral cholinergic syndrome was induced in mice by oxotremorine administration; pretreatment orally with cytidine diphosphocholine (CDP-choline) does not potentiate this syndrome and even antagonizes oxotremorine-induced salivation. Levodopa antagonizes the oxotremorine-induced cerebral symptoms (akinesia + tremor); however this antagonism disappears when mice are chronically pretreated orally with CDP-choline, confirming the action of CDP-choline on dopaminergic pathways. The proven efficacy of CDP-choline in Parkinsonism could then be mediated by a hypersensitivity of some cerebral dopamine receptors, and not by a direct stimulating effect of the striatal dopaminergic receptors.

Effects of parenteral treatment by nicergoline on the development of hypertension of S.H.R.

Six consanguine monogamous SHR couples (G 1) were treated from 5 weeks of age on with an alpha blocker, nicergoline, 100 mcg. kg-1 day-1 i.p. Male rats were treated without interruption; treatment was withheld in female rats from delivery to weaning. They were compared with six similar SHR couples who were only daily i.p. injected with the same volume of solvent in the same conditions, as controls. Second (G 2) and third (G 3) generation rats (untreated) were studied. In G 1 rats, systolic blood pressure (SBP) was decreased, and no change was found in heart rate (H R), heart weight to body weight ratio (HW/BW), hypothalamic and bulbar noradrenaline content (HNA,BNA). In G 2 rats, SBP, BNA and plasma renin activity were significantly decreased, all other parameters being unchanged. No parameter change was observed in G 3 rats. We think that such long acting effects after antenatal treatment could only be due to an action on the origin of the SHR hypertension.

Physicochemical, pharmacological and pharmacokinetic study of a new GABAergic compound, calcium acetylhomotaurinate.

It has been shown that calcium acetylhomotaurinate (Ca AOTA; Meram Patent, France) decreased voluntary ethanol intake in rats (1); this was antagonized by bicuculline. Homotaurine did not have this effect. We thought this was due to a different blood-brain barrier crossing ability for the two drugs. The present study was, therefore, planned to confirm blood-barrier crossing by Ca AOTA and to study the drug's physicochemical and pharmacokinetic characteristics. Both in vitro and in vivo (i.p.) administration of Ca AOTA increased the accumulation of [3H] GABA in rat striatal synaptosomal preparations. The chemical study confirmed Ca AOTA's great stability in biological and hydrophilic media, excluding a "homotaurine-dispensing" effect. The molecule was totally dissociated in such media, but the absence of any detectable acid form at any pH indicates that ion pairs are formed to cross barriers, and/or that a carrier system is used. The pharmacokinetic study showed short half-lives (5 and 30 min for the distribution and elimination phases) and small distribution volumes. However, the elimination phase distribution volume was dose-dependent, a further argument for a carrier transport system. From the present study it appears that Ca AOTA is an extremely stable drug, totally dissociated in hydrophilic media, which acts centrally as a GABA agonist after crossing the blood-brain barrier. It is not a precursor of homotaurine and presumably crosses barriers with the help of a transporter.