Pinealectomy and Exogenous Melatonin Regulate Anxiety-Like and Depressive-Like Behaviors in Male and Female Wistar Rats

The main objective of this work was to 1) study the influence of endogenous melatonin (Mel) abolishment via pinealectomy and 2) explore exogenous Mel effect on anxiety-like and depressive-like behavior in male and female rats. Rats were shamoperated (Sh) or pinealectomized (Px) and following subgroups were selected 1) Px/NaCl (0.9%) and Sh/NaCl (0.9%) : rats injected subcutaneously, once daily for 8 weeks, with saline solution NaCl (0.9%) as vehicle;2) Px/Mel (4 mg/Kg) and Sh/Mel (4 mg/Kg): Rats similarly injected with 4 mg/Kg of Mel. All animals were housed under a photoperiod of (LD:16/8). After different treatments animals were tested in the open-field test (OFT), elevated plus maze test (EPM) to determine anxiety-like behavior, and forced swimming test (FST) to evaluate depressive-like level. Our results revealed that level of anxiety-like and depressive-like behavior are significantly higher in Px/NaCl (0.9%) when compared to Sh/NaCl (0.9%) group, suggesting that pinelectomy induced an anxiogenic and depressant effects. The Px effects would be due to the absence of endogenous Mel synthesis and release. Additionally, we clearly demonstrated that the level of anxiety-like and depressive-like behavior are higher in Px/Mel (4 mg/Kg) and Sh/Mel when compared respectively to Px/NaCl (4 mg/Kg) and Sh/NaCl groups suggesting an anxiolytic and antidepressant effects of exogenous Mel. Behavioral responses were sex dependent since the difference between females and males, especially, after melatonin administration, were statistically significant. These experiments provide evidence that pinealectomy and Mel regulated emotionally behavior in male and female rats.

Effects of Pinealectomy and Gonadectomy on Olfactory Bulb Dopaminergic Neurons in Rats

Background： Olfactory disorder is an early manifestation of Parkinson＆#39;s disease （PD）, likely to be associated with abnormalities of the dopaminergic neurons in the olfactory bulb （OB）; however, the causes of olfactory disorder in PD are not entirely clear. Some studies showed that melatonin （MT） and androgens （mainly testosterone, T） might participate in the pathogenesis of PD. The research aimed to investigate effects of MT or T deficiency on OB dopaminergic neurons in rats. Methods： One hundred and twenty normal male Wistar rats were randomly divided into the control, sham operation pinealectomy （PX）, sham operation gonadectomy （GDX）, PX, GDX, and PX ＋ GDX groups. After 60 days, glial cell hyperplasia and neuronal apoptosis were examined with hematoxylin and eosin and the TUNEL method; the expression levels of tyrosine hydroxylase （TH）, Bax, and Bcl-2 were measured using immunohistochemistry （IH） by the streptavidin peroxidase conjugated method. Comparison among multiple sets used analysis of variance and LSD method or Kruskal-Wallis test and Nemenyi method. Results： There were no significant differences between the sham operation groups and the control group; thus, they were merged into Group A. There was no significant glial cell hyperplasia （P 〉 0.05） or change in shape in any of the groups after PX or GDX. The number of apoptotic cells in Groups A （1.41 ± 0.56）, PX （12.31 ± 4.68）, GDX （20.52 ± 5.13）, and PX ＋ GDX （30.23 ± 5.25） successively significantly increased （P 〈 0.05）. The number of TH （＋） cells in Groups A （42.62 ± 5.63）, PX （37.31 ± 4.32）, GDX （31.07 ± 4.21）, and PX ＋ GDX （25.22 ± 3.66） was successively significantly decreased （P 〈 0.05）. The gray value of TH （＋） cells and fibers in Groups A （98.51 ± 10.36）, PX （108.96 ± 13.01）, GDX （119.02 ± 12.98）, and PX ＋ GDX （128.99 ± 13.39） was successively significantly increased （P 〈 0.05）. The results of Bax staining were as follows： Group A＋, Group PX＋＋, Group GDX＋＋, and Group PX＋ GDX＋＋＋, the results of Bcl-2 in all groups were ＋. Conclusions： PX or GDX could lead to OB neurotoxicity in the following groups of rats in the following order： PX 〈 GDX 〈 PX ＋ GDX. PX or GDX increased the ratio of Bax/Bcl-2. The effect of PX and GDX was equal, but both were less than that of PX ＋ GDX. Neurotoxicity as a result of PX or GDX was not related to inflammation.

Effects of Melatonin Levels on Neurotoxicity of the Medial Prefrontal Cortex in a Rat Model of Parkinson＇s Disease

Background： Damage of the medial prefrontal cortex （mPFC） results in similar characteristics to the cognitive deficiency seen with the progress of Parkinson＇s disease （PD）. Since the course of mPFC damage is still unclear, our study aimed to investigate the effects of melatonin （MT） on neurotoxicity in the mPFC of a rat model of PD. Methods： One hundred and fifty-four normal, male Wistar rats were randomly divided into the following five groups： normal ＋ normal saline （NS）, normal ＋ 6-hydroxydopamine （6-OHDA）, sham pinealectomy （PX） ＋ 6-OHDA, PX ＋ 6-OHDA, and MT ＋ 6-OHDA. 6-OHDA was injected into the right substantia nigra pars compacta （SNc） and ventral tegmental area （VTA） of each group, except normal ＋ NS, 60 days after the PX. In the MT treatment group, MT was administered immediately after the intraperitoneal injection at 4 p.m. every day, for 14 days. Neuronal apoptosis in the mPFC was exalnined using the TUNEL method, while the expression oftyrosine hydroxylase （TH）, Bax, and Bcl-2 in this region was measured using immunohistochemistry. The concentration of malondialdehyde （MDA） in the mPFC was examined using the thioharbituric acid method. Results： Rats in the normal ＋ 6-OHDA and sham PX ＋ 6-OHDA groups were combined into one group （Group N ＋ 6-OHDA） since there was no significant discrepancy between the groups for all the detected parameters. Apoptosis of cells in the NS, MT ＋ 6-OHDA, N ＋ 6-OH DA, and PX ＋ 6-OHDA groups was successively significantly increased （Hc = 256.25, P 〈 0.001 ）. The gray value of TH （＋） fibers in the NS, MT ＋ 6-OHDA, N ＋ 6-OHDA, and PX ＋ 6-OHDA groups was also successively significantly increased （F= 99.33, P 〈 0.001 ）. The staining intensities of Bax and Bcl-2 were as follows： Group NS ＋/＋, Group MT ＋ 6-OHDA ＋＋/＋, Group N ＋ 6-OHDA ＋＋/＋, and PX ＋ 6-OHDA ＋＋＋/＋. The concentrations of MDA in the NS, MT ＋ 6-OHDA, N ＋ 6-OHDA, and PX ＋ 6-OHDA groups were significantly increased in sequence （Hc = 296.309, P 〈 0.001 ）. Conclusions： Neuronal damage of the VTA by 6-OHDA might induce VTA-mPFC nerve fibers to undergo anterograde nerve damage, in turn inducing transneuronal damage of the mPFC. PX significantly exacerbated the neurotoxicity in the mPFC, which was induced by the neuronal injury of the VTA. However, MT replacement therapy significantly alleviated the neurotoxicity in the mPFC.