Estrogen protects the dopaminergic neurons in substantia nigra against damage induced by 6-hydroxydopamine / 生理学报

Substantial evidence strongly implies that sensory gating P50 (also called P50 auditory evoked potential, P50) and dopaminergic neurotransmitters are related. In animal experiment, P50 can be recorded in an awake and quiet state with freedom of movement. Until now there is lack of animal experimental data on the supportive effect of estrogen on function of dopaminergic neurons in substantia nigra (SN) in physiological state. In the present study, female Sprague-Dawley (SD) rats were used as subjects. The animals were divided randomly into four groups: (1) control group (normal animals); (2) Parkinson's disease (PD) model group: the right SN was lesioned with 6-hydroxydopamine (6-OHDA); (3) PD model with bilateral ovariectomized group (OVX-PD): bilateral ovariectomy was performed before administration with 6-OHDA; (4) estrogen + PD model with bilateral ovariectomized group (OVX-E(2)-PD): physiological dose of estrogen was given to the bilateral ovariectomy animals before administration with 6-OHDA. P50 induced by two brief acoustic stimuli were recorded in the right SN and the number of TH(+) dopaminergic neurons in the SN stained by immunohistochemistry was calculated after the determination of P50. The results showed that in the PD model group, the testing/conditioning (T/C) ratio of P50 decreased by 40.60% and the number of TH(+) cells in the right SN decreased by 64.74% as compared with that in the control group (P<0.01); In the OVX-PD group, the T/C ratio of P50 decreased by 45.88% and the number of TH(+) cells was reduced by 57.26% as compared with that in the PD group (P<0.01). Administration with 6-OHDA into the SN pars compacta of ovariectomized rats caused more decrease in the number of TH(+) cells as well as more damage to the function of sensory gating in SN. While in OVX-E(2)-PD group, intramuscular injection with estrogen at physiological dose 3 d before 6-OHDA administration decreased the degree of damage to the SN functionally and morphologically, and its degree of injury corresponded to PD group. These results indicate that the mechanism of protection of dopaminergic neurons in the SN provided by physiological level of estrogen is by promoting the resistibility of the neurons to harmful stimulation. If the gonads are resected resulting in a lack of estrogen, the degree of injury to the function and morphology of dopaminergic neurons in SN induced by 6-OHDA increases. Replacement of estrogen at physiological level on time is necessary. Sensory gating P50 in SN may reflect dynamically the protection of estrogen against dopaminergic neurons depletion in vivo.

Sexual dimorphisms of dopaminergic neurons in rat substantia nigra / 生理学报

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. Sixty 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) Ovariectomized + estrogen-replaced group (OVX-E(2) group): The rats received sequentially physiological dose of estrogen for 3 d from the 7th day after ovariectomization. P50 auditory evoked potential (P50) was recorded for 14 d from electrodes inserted in the rat right SN 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 normal female rats (P<0.05), and the T/C ratio of P50 in normal males was significantly less than that in normal females (P<0.01), indicating that there exists sexual difference in function and structure in the SN. No differences in the T/C ratio of P50 or the number of TH(+) cells were found between M-INT and CAST groups. The 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 the T/C ratio of P50 and the number of TH(+) cells in the SN between OVX- E(2) and F-INT groups 15-20 d after estrogen replacement, suggesting that estrogen can promote the survival and functional recovery of dopaminergic neurons in the SN. The results suggest that there exist sex-specific differences in the dopaminergic neurons in the SN structurally and functionally. The difference of estrogen level in cerebra between male and female animals may account for the sexual differences. Endogenous estrogen plays an important role in maintaining the integrity and modulating the functional activity of dopamine system in the SN.