In vivo changes in responsiveness of the caudate nucleus to L-dopa infusion as a function of the estrous cycle.
In the present experiment we measured changes in the responsiveness of the nigrostriatal dopaminergic system to L-DOPA as a function of the estrous cycle in the freely behaving animal with push-pull perfusion. Intact female rats were implanted with a push-pull cannula directed at the caudate nucleus and perfused repetitively on each day of their estrous cycle. During the perfusion, the response of the caudate nucleus was tested with two successive increasing doses of L-DOPA (1.0 and 10 microM) infused directly through the push side of the cannula. In response to 1.0 microM L-DOPA, significantly greater dopamine release was obtained for female rats perfused on proestrus, with all 6 females showing maximal responsiveness at this estrous cycle stage. There was an overall 3-4 fold greater increase in dopamine release to the 10 microM L-DOPA infusion, regardless of estrous cycle day. However, with the use of this 10 microM L-DOPA dose, the significant effect at proestrus was maintained. These results demonstrate that the responsiveness of the caudate nucleus to L-DOPA is maximal at proestrus. These data together with previous work from our laboratory indicate that the natural physiological changes which occur in hormone levels, in particular changes in progesterone during proestrus, exert a substantial influence upon this extra-hypothalamic central nervous system site.
Dluzen
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Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
Ramirez
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D000818:Animals; D002404:Catheterization; D002421:Caudate Nucleus / Q000187:drug effects*; D004298:Dopamine / Q000502:physiology; D004971:Estrus / Q000502:physiology*; D005260:Female; D012739:Gonadal Steroid Hormones / Q000502:physiology; D007263:Infusions, Parenteral; D007980:Levodopa / Q000494:pharmacology*; D010477:Perfusion; D051381:Rats
D012739:Gonadal Steroid Hormones; D007980:Levodopa; D004298:Dopamine