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  • 1
    Electronic Resource
    Electronic Resource
    Time-dependent effects of ovarian steroids on tyrosine hydroxylase activity in the limbic forebrain of female rats (1991)
    Springer
    Journal of neural transmission 83 (1991), S. 77-84 
    Details
    ISSN: 1435-1463
    Keywords: Estradiol ; progesterone ; limbic forebrain ; tyrosine hydroxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In this work, we have studied the time-course of the effects of pharmacological administration of ovarian steroids on tyrosine hydroxylase (TH) activity in the limbic forebrain of ovariectomized rats. Administration of estradiol produced a late decrease in TH activity. This effect was found 24 hours after the last steroid injection, disappearing at 32 hours. It was antagonized by progesterone, since a single injection of this steroid to estradiol-pretreated rats reversed to control values the estradiol-induced decrease. Nevertheless, the administration of progesterone after estradiol treatment caused a short-time decrease in the limbic activity of TH, which was observed 4 hours after the last steroid injection, disappearing subsequently. On the other hand, the administration of progesterone alone produced a biphasic effect, with a reduction at 24 hours, followed by an increase at 32 hours. These effects were only observed in the animals non-treated with estradiol, disappearing with a previous treatment with estrogens. Hence, it can be concluded that both ovarian steroids may affect the limbic TH activity. Thus, estradiol produced a late inhibitory effect on the activity of this enzyme, which was antagonized by progesterone. Administration of the last one to estradiol-treated rats produced a short-time inhibitory effect, whereas its administration to non-treated rats produced a late biphasic effect (inhibition followed by stimulation), which was not observed in estradiol-treated rats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01244454
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  • 2
    Electronic Resource
    Electronic Resource
    Nigrostriatal and mesolimbic dopaminergic activities were modified throughout the ovarian cycle of female rats (1991)
    Springer
    Journal of neural transmission 85 (1991), S. 223-229 
    Details
    ISSN: 1435-1463
    Keywords: Sexual steroids ; estrous cycle ; limbic forebrain ; striatum ; dopamine ; DOPAC ; tyrosine hydroxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In this work, we have studied the changes in the functional state of nigrostriatal (NSDA) and mesolimbic (MLDA) dopaminergic neurons during the estrous cycle of the female rat. The activity of tyrosine hydroxylase (TH), the turnover rate (Kt) after inhibition of dopamine (DA) synthesis and the ratio between the contents of this amine and its metabolite, L-3,4 dihydroxyphenylacetic acid (DOPAC), were used as indices of neuronal activity. The neuronal activity of NSDA neurons rose during estrous and declined during proestrous, as reflected by the values of Kt and DOPAC/DA ratio measured during both phases. Interestingly, the course of variations in striatal TH activity was similar, although retarded in relation to the changes in neuronal activity. Thus, TH activity was high during diestrous, whereas it was low during estrous. The activity of MLDA neurons was reduced during proestrous. This can be concluded from the decreased Kt and DOPAC/DA ratio measured in this phase and it was accompanied by a low TH activity. Thereupon, both Kt and TH activity increased during estrous. These results indicate the existence of physiological changes in the functional state of both dopaminergic systems during the ovarian cycle, which are partially different for each neuronal pathway. This supports the existence of a specific regulation, and not indiscriminate effects, by the hormones involved in this cycle, mainly estradiol and progesterone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01244947
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  • 3
    Electronic Resource
    Electronic Resource
    Modifications of mesolimbic and nigrostriatal dopaminergic activities after intracerebroventricular administration of prolactin (1994)
    Springer
    Journal of neural transmission 96 (1994), S. 63-79 
    Details
    ISSN: 1435-1463
    Keywords: Prolactin ; striatum ; limbic forebrain ; dopamine ; DOPAC ; tyrosine hydroxylase ; D1 and D2 receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the present study we examined the effects of intracerebroventricular (i.c.v.) injections of prolactin (PRL) on the presynaptic activity and postsynaptic sensitivity of mesolimbic and nigrostriatal dopaminergic neurons. In addition, the effects of PRL onin vitro release of dopamine (DA) from perifused striatal fragments were examined. Tyrosine hydroxylase (TH) activity and D2 receptor density in the striatum decreased after i.c.v. PRL administration; this was accompanied by an increase in D2 receptor affinity. These effects occurred after i.c.v. administration of PRL to normoprolactinemic rats, although normally they did not appear after administration to animals with pituitary grafting-induced hyperprolactinemia. Thus, in these animals, i.c.v. PRL failed to decrease TH activity and D1 and D2 receptor densities to a significant extent. In the case of D2 receptors, this was probably due to the fact that pituitary grafting-induced hyperprolactinemia itself was able to reduce the density of this receptor. No changes were observed in DA or L-3, 4-dihydroxyphenylacetic acid (DO-PAC) contents after i.c.v. administration of PRL to both normo- and hyperprolactinemic animals. Basal and K+-evoked DA releasein vitro from perifused striatal fragments of normoprolactinemic rats were not affected by the addition of PRL, whereas this hormone enhanced K+-evoked DA release when added to perifused striatal fragments from hyperprolactinemic animals. In the limbic forebrain, i.c.v. administration of PRL to normoprolactinemic animals produced a decrease in DA and DOPAC contents and D1 receptor density. Interestingly, none of these effects appeared when PRL was injected to hyperprolactinemic animals. In summary, our results suggest a possible inhibitory role of PRL on the activity of both the nigrostriatal and mesolimbic dopaminergic neuronal systems. These inhibitory effects were reflected in the decreases elicited in a set of neurochemical parameters, indicating either presynaptic activity or postsynaptic sensitivity, after i.c.v.-administered PRL. This observation supports the hypothesis of a possible neuromodulatory role for an extrapituitary PRL on the activity of these neurons, although the fact that most of these effects did not appear when i.c.v. administration was performed in hyperprolactinemic rats also suggests that they are influenced by peripheral PRL levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01277929
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  • 4
    Electronic Resource
    Electronic Resource
    δ9-Tetrahydrocannabinol affects mesolimbic dopaminergic activity in the female rat brain: interactions with estrogens (1993)
    Springer
    Journal of neural transmission 92 (1993), S. 81-95 
    Details
    ISSN: 1435-1463
    Keywords: δ9-Tetrahydrocannabinol ; mesolimbic dopaminergic neurons ; estrogens ; dopamine ; dopaminergic receptors ; limbic forebrain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In this work, we studied the possible estrogenic modulation of the effects of δ9-tetrahydrocannabinol (THC) on mesolimbic dopaminergic activity, by examining the effects of an acute dose of this cannabinoid: (i) during the estrous cycle; (ii) after ovariectomy, chronic estrogen-replacement and tamoxifen (TMX)-induced blockade of estrogenic receptors; and (iii) combined with a single and physiological injection of estradiol to ovariectomized rats. THC significantly decreased the density of D1 dopaminergic receptors and non-significantly increased the L-3,4-dihydroxyphenylacetic acid (DOPAC) content in the limbic forebrain of ovariectomized rats chronically replaced with estrogens. The decrease in D1 receptors was also produced by TMX, whereas the coadministration of both THC and TMX did not lead to a major decrease. In addition to the trend of THC increasing DOPAC content, this cannabinoid was also able to increase the ratio between DOPAC and dopamine, although this last effect only occurred after coadministration of THC and TMX, which had been ineffective administered individually. All these effects were not seen when THC was administered to normal cycling rats during each phase of estrous cycle and to ovariectomized rats without chronic estrogen replacement or only submitted to a single and acute dose of estradiol. This observation might be related to the fact that the density of limbic cannabinoid receptors increased in chronic estrogen-replaced ovariectomized ratsversus normal cycling, ovariectomized or acutely estrogen-treated ovariectomized rats. Interestingly, THC administration in ovariectomized rats was followed by a slight, although significant, increase in tyrosine hydroxylase activity, which was also observed after coadministration of THC with a short-time and acute dose of estradiol. In summary, THC stimulated the presynaptic activity of mesolimbic dopaminergic neurons, but accompanied by a decrease in their postsynaptic sensitivity. These effects did not appear in normal cycling rats being only evident after ovariectomy and chronic estrogen replacement, which might be related to changes in binding characteristics of cannabinoid receptors in this area. Moreover, some of them appeared after TMX-induced blockade of estrogenic cytosolic receptors, which likely suggests the existence of a certain estrogenic modulation of the actions of THC on mesolimbic neurons. On the contrary, coadministration of THC with a single and shortly tested dose of estradiol was always ineffective in modifying THC effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01244868
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    Paper (German National Licenses)
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