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Sexual dimorphisms of dopaminergic neurons in rat substantia nigra

Ma Yuanyi, Kong Shuzhen, Yang Lijiang, Meng Jinlan, Lu Lechun, He Min

Department of Physiology, Kunming Medical College.Kunming 650031,Yunnan

Abstract

There are sex differences in some brain areas in mammalians. Parkinson's disease (PD), caused by the mesencephalic substantia nigra (SN) dopaminergic neuronal loss, displays sexual difference, i.e., the incidence is higher and the symptoms are more intense in males than that in females. However, it has not been known whether sexual dimorphisms exist in the SN, which reflects the male preponderance. To explore the mechanism of the difference, 60 adult Sprague-Dawley rats were randomly divided into 5 groups: (1) female intact group (F-INT group); (2) male intact group (M-INT group); (3) ovariectomized group (OVX group); (4) castration group (CAST group); (5) ovariectomy + estrogen-replaced group (OVX-E_(2) group). The rats received sequentially physiological dose of estrogen for 3 d after ovariectomization for 7 d. P50 auditory evoked potentials were recorded for 14 d from electrodes inserted in the right SN of the rats in quiet and awake state. After recording, the brain tissues were dissected and the tyrosine hydroxylase (TH)-expressing neurons in the compact zone of the SN were counted using immunohistochemical method. The results showed that the number of TH-positive (TH~(+)) cells in the SN of normal male animals was less than that in female rats (P<0.05), and the T/C ratio of P50 in males was significantly less than that in females (P<0.01), indicating that there exists sexual difference in function and structure in the SN. No differences in T/C ratio of P50 or the number of TH+ cells were found between M-INT and CAST groups. T/C ratio of P50 and the number of TH~(+) cells in the SN in OVX group were reduced significantly compared with those in F-INT group (P<0.01). There was no significant difference in T/C ratio of P50 and the number of TH+ cells in the SN between OVX-E_(2) and F-INT groups (P>0.05) 15-20 d after estrogen replacement. These results indicate that estrogen can promote survival of the dopamine neurons and recovery of function of these neurons in the SN. Conclusion: The results in the present study suggest that there exist sex-specific differences in the dopaminergic neurons in the SN structurally and functionally. Different levels of estrogen in cerebra between male and female animals may account for the sex differences. Endogenous estrogen plays an important role in maintaining the integrity and modulating the functional activity of dopamine system in the SN.

Key words: sex dimorphisms in brain;Estrogen;Substantia nigra;dopaminergic neuron;sensory gating;P50 auditory evoked potential;tyrosine hydroxylase

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Citing This Article：

Ma Yuanyi, Kong Shuzhen, Yang Lijiang, Meng Jinlan, Lu Lechun, He Min. Sexual dimorphisms of dopaminergic neurons in rat substantia nigra. Acta Physiol Sin 2007; 59 (6): 753-758 (in Chinese with English abstract).