Comparison of alpha-synuclein immunoreactivity and protein levels in ischemic hippocampal CA1 region between adult and aged gerbils and correlation with Cu,Zn-superoxide dismutase.

In this study, we examined changes in the level and immunoreactivity of alpha-synuclein in the hippocampal CA1 region of adult (6 months old) and aged (24 months old) gerbils after 5 min of transient forebrain ischemia. The delayed neuronal death of CA1 pyramidal cells in adult gerbils was severer than that in aged gerbils 4 days after ischemia/reperfusion. Alpha-synuclein immunoreactivity in the CA1 region of adult and aged gerbils significantly changed after ischemia. In control animals, alpha-synuclein immunoreactivity and level in the aged-gerbil CA1 region were higher than those in the adult-gerbil CA1 region. In both adult and aged gerbils, alpha-synuclein immunoreactivity and level started to increase 3h after ischemia, and they were highest 1 day after ischemia. Thereafter, alpha-synuclein immunoreactivity and level decreased with time after ischemia. We also observed the effects of Cu,Zn-superoxide dismutase (SOD1) on ischemic damage using the Pep-1 transduction domain. Alpha-synuclein level in the CA1 region was lower in Pep-1-SOD1-treated adult and aged gerbils than in vehicle-treated adult and aged gerbils. We conclude that neuronal loss in the hippocampal CA1 region of adult gerbils was more prominent than that in aged gerbils 4 days after ischemia/reperfusion. The higher level of alpha-synuclein in the aged-gerbil CA1 region than that in the adult-gerbil CA1 region may be associated with the earlier induction of reactive oxygen species, and Pep-1-SOD1 potentially and reversibly inhibits the accumulation of alpha-synuclein in the CA1 region after transient ischemia.

Seizure-induced changes of mineralocorticoid and glucocorticoid receptors in the hippocampus in seizure sensitive gerbils.

Abnormal corticosteroid hormone levels during stress and resultant mineralocorticoid receptor (MR)/glucocorticoid receptor (GR) imbalance enhance the vulnerability of specific hippocampal neurons. In the present study, we investigated the distribution of MR and GR in seizure resistant (SR) and seizure sensitive (SS) gerbils, and observed the seizure-induced changes of MR and GR in the hippocampus of SS gerbils using immunohistochemistry and western blot analysis. MR and GR immunoreactivities were higher in the SS pre-seizure gerbils than that in SR gerbils. In the SR gerbils, the immunodensity of GR was high compared to that of MR. The changes of MR and GR immunoreactivities were significant in the stratum pyramidale of the hippocampal CA1 region and the infrablade of the dentate gyrus after seizure on-set. MR immunoreactivity in the CA1 region was significantly increased at 12h after seizure on-set, thereafter MR immunoreactivity was decreased. MR immunoreactivity in the dentate gyrus was decreased time-dependently after seizure on-set. GR immunoreactivity was decreased in the CA1 region and dentate gyrus time-dependently after seizure on-set. At 12h after seizure on-set, differences in MR and GR immunodensity diminished in the CA1 region and dentate gyrus. This imbalance of MR and GR immunoreactivity in these regions may be associated with seizure generation in the Mongolian gerbil, which is a hereditary seizure model.

Soy isoflavones and cognitive function.

There is growing interest in the physiological functions of soy isoflavones, especially in whether they affect cognitive function and have beneficial effects on neurodegenerative diseases. Here we review the recent evidence from clinical and experimental studies supporting a role for soy isoflavones in cognitive function. Soy isoflavones may mimic the actions and functions of estrogens on brain, and they have been shown to have positive effects on the cognitive function in females; however, studies on their effects on spatial memory have not provided consistent results in males. Although data from humans, cultures, and animal models are currently insufficient for elucidating the metabolism of soy isoflavone actions on cognitive function and the nervous system, we suggest two putative pathways; (1) an estrogen receptor-mediated pathway and (2) via the inhibition of tyrosine kinase, in particular by genistein, which is one of the soy isoflavones. Although soy isoflavones appear to have a positive effect on brain function, further research is needed to determine not only the efficacy but also the safety of soy isoflavones on the nervous system and cognitive function.

Age-related changes of parvalbumin immunoreactive neurons in the rat main olfactory bulb.

Parvalbumin (PV) is found in the olfactory system, including the main olfactory bulb, and is thought to be one of the neuroactive substances in olfaction. Changes in PV immunoreactivity in the olfactory system during aging have not been examined. We investigated such changes in the main olfactory bulb (MOB) of the rat at postnatal month 1 (PM 1), PM 3, PM 6, PM 12 and PM 24. PV-IR neurons were almost completely restricted to the external plexiform layer. At PM 1 there were only a few PV-IR neurons; at PM 3, the number of PV-IR neurons was at its greatest but they were not well developed morphologically. At PM 6, the number of PV-IR neurons was similar to that at PM 3 and they had satellite somata with well-developed processes with many varicosities. By PM 12 the number of neurons and processes had declined, and by PM 24, they had fallen even further and the remaining processes had lost most of their varicosities. We conclude that age-related degeneration of PV-IR neurons in the MOB may reduce calcium buffering and affect olfactory function in senile species.

Chronological alterations of calbindin D-28k immunoreactivity in the gerbil main olfactory bulb after ischemic insult.

We investigated spatial and temporal alterations of calbindin D-28k (CB) immunoreactivity in the gerbil main olfactory bulb after transient ischemia-reperfusion. In sham-operated animals, CB-immunoreactive (IR) neurons were found in the periglomerular layer, external plexiform layer and granule cell layer. At 1-4 days after ischemic insult, the number of CB-IR neurons significantly increased. This result suggests that the increased CB may buffer the intracellular calcium at an early time point after the ischemic insult. In contrast, 10-30 days after the ischemic insult, the number of CB-IR neurons significantly decreased as compared to sham-operated animals. This result suggests that a malfunction in olfactory process may have occurred in the olfactory bulb at a later time point after the ischemic insult.

Effects of exposure to genistein and estradiol on reproductive development in immature male mice weaned from dams adapted to a soy-based commercial diet.

Genistein, a soybean-originated isoflavone, is widely consumed by humans for putative beneficial health effects but its estrogenic activity may adversely affect the development of male reproductive system. Twenty one-day-old ICR mice weaned from dams fed with a soybean-based diet throughout gestation and lactation were exposed by gavage to genistein (2.5 mg/kg b.w./day) or 17beta-estradiol (7.5 microg/kg b.w./day) for five weeks. Corn oil was used as a negative control. The animals were fed with a casein-based AIN-76A diet throughout the experimental periods. There were no significant differences in body and organ weights of mice among experimental groups. No significant differences in sperm counts and sperm motile characteristics were found between control and genistein groups. Treatment of 17beta-estradiol caused a significant decrease in prostate weight and epididymal sperm counts compared to the control (p<0.05). The levels of phospholipid hydroxide glutathione peroxidase in the testis and prostate of mice exposed to genistein or 17beta-estradiol were significantly higher than that of the control mice (p<0.05). 17beta-estradiol treatment caused degeneration and apoptosis of germ cells in the testis, depletion and degeneration in the epididymal epithelium, and hyperplasia of mucosal fold region in the prostate of mice. Genistein treatment did not cause any lesion in the testis, epididymis, and prostate. These results suggest that dietary uptake of genistein during juvenile period may not affect male reproductive development and functions.

Exposure to genistein does not adversely affect the reproductive system in adult male mice adapted to a soy-based commercial diet.

Genistein, a soybean-originated isoflavone, is widely consumed by humans for putative beneficial health effects but its estrogenic activity may affect adversely the development of male reproductive system. Five-week-old ICR mice were purchased and fed with a soybean-based Purina Chow diet until 6 months of age. The animals were exposed by gavage to genistein (2.5 mg/kg/day) or 17beta-estradiol (7.5 microg/kg/day) for five weeks. Corn oil was used for the negative control. The animals were fed the casein-based AIN-76A diet throughout the experimental periods. There were no significant differences in body and organ weights of mice among experimental groups. No significant differences in sperm counts and sperm motile characteristics were found between the control and the genistein groups. Treatment of 17beta-estradiol caused a significant decrease in epididymal sperm counts compared to the control (p<0.05). The level of phospholipid hydroxide glutathione peroxidase in the epididymis of mice exposed to genistein was significantly higher than that of the control mice (p<0.05). 17beta-estradiol treatment caused a reduction of germ cells in the testis and hyperplasia of mucosal fold region in the prostate of mice. Genistein treatment did not cause any lesion in the testis, epididymis, and prostate. These results suggest that dietary uptake of genistein at adult stage of life may not affect male reproductive system and functions.

Effects of soy phytoestrogens on reference memory and neuronal cholinergic enzymes in ovariectomized rats.

The effects of soy phytoestrogens on Morris water maze (MWM) performance and neuronal cholinergic enzyme activities and immunoreactivity were studied in ovariectomized (OVX) rats. The rats were assigned to four groups fed control diet (CD), 3.9 mg/kg 17beta-estradiol diet (E2), 263.4 mg/kg soy phytoestrogens diet (SP1), and 526.9 mg/kg soy phytoestrogens diet (SP2). In the MWM task, escape latency and path length were significantly less in the E2 and SP2 groups than in the CD group on the second day. Choline acetyltransferase (ChAT) activity in the cerebral cortex and ChAT immunoreactivity in the diagonal band of Broca were significantly greater in the E2, SP1, and SP2 groups than in the CD group. Acetylcholinesterase activity in the hippocampus in the E2, SP1, and SP2 groups was significantly lower than in the CD group. This study suggests that soy phytoestrogens affect the reference memory and neuronal cholinergic system in OVX rats.

Soy isoflavones mitigate long-term femoral and lumbar vertebral bone loss in middle-aged ovariectomized mice.

We evaluated the protective effects of soy isoflavones (SIF) against osteoporosis in middle-aged ovariectomized (OVX) mice. SIF (30 mg/kg or 60 mg/kg) or 17beta-estradiol (E(2)) was administered to OVX mice for 4 months after bilateral ovariectomy. We observed the biochemical markers of bone turnover, e.g., alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP), in serum. We also observed the bone mineral density (BMD) in femurs and lumbar vertebrae. In addition, we examined trabecular bone and interstitial cells in the femur using hematoxylin and eosin staining. The decrease in ALP levels and the increase in TRAP levels normally resulting from ovariectomy were suppressed by administration of 60 mg/kg SIF or E(2). Administration of 60 mg/kg SIF or E(2) also maintained the BMD, trabecular bone, and interstitial cells in OVX mice compared to those in pre-OVX mice. These results suggest that 60 mg/kg SIF effectively mitigates ovariectomy-induced osteoporosis in middle-aged mice.

Soybean isoflavones alter parvalbumin in hippocampus of mid-aged normal female, ovariectomized female, and normal male rats.

AIM: To investigate the long-term effect of soybean isoflavones on changes in parvalbumin (PV) immunoreactivity in the hippocampus in normal female, ovariectomized (OVX) female and normal male rats. METHODS: Ten-month-old rats were assigned to one of 9 groups (n = 7 in each group) based on body weight using a randomized complete-block design. The groups were: control diet-treated females, OVX females, and males; 0.3 g/kg isoflavone-treated females, OVX females, and males; and 1.2 g/kg isoflavone-treated females, OVX females, and males. The PV immunostaining was conducted by using the standard avidin-biotin complex method. RESULTS: PV immunoreactivity and the number of PV-immunoreactive neurons in all the groups after isoflavone treatment were significantly changed in the hippocampal CA1 region and in the dentate gyrus, but not in the hippocampal CA2/3 region. PV immunoreactivity and the number of PV-immunoreactive neurons in the control diet OVX females were similar to those in the control diet, and were greater than those in the control diet normal females. PV immunoreactivity and the number of PV-immunoreactive neurons in all the isoflavone-treated groups decreased dose-dependently after isoflavone treatment. CONCLUSION: Long-term administration of isoflavones may induce a reduction of PV in interneurons in the hippocampal CA1 region and in the dentate gyrus. The reduction of PV in these regions suggests that the long-term administration of isoflavones may cause a change in calcium homeostasis in the hippocampal CA1 region and in the dentate gyrus.

Calbindin D-28k immunoreactivity increases in the hippocampus after long-term treatment of soy isoflavones in middle-aged ovariectomized and male rats.

This article investigates the long-term effects of soybean isoflavones (ISO) on the changes of calbindin D-28k (CB) immunoreactivity in the hippocampus in middle-aged ovariectomized female rats as well as middle-aged control female and male rats to identify any correlation between calcium and phytoestrogens. In the CA1 region, CB immunoreactivity in the ovariectomized females was similar to that of the control females, whereas CB immunoreactivity in the males was significantly lower than that of the control females. In the dentate gyrus, CB immunoreactivity in the ovariectomized females and males was significantly lower than that of the control females. CB immunoreactivity in all groups was increased dose-dependently after ISO treatment in the CA1 region and dentate gyrus. This result suggests that ISO treatment enhances the expression of CB immunoreactivity in the hippocampus in the middle-aged rats.

Evaluation of the preventive effect of isoflavone extract on bone loss in ovariectomized rats.

To examine a potential role for soybean phytoestrogens in postmenopausal bone loss, twenty-four 12-week-old Sprague-Dawley rats were divided randomly into 4 groups and given controlled diets for 16 weeks. The treatment groups were as followed: sham operated, ovariectomized (OVX) control, OVX + isoflavone extract (6.25 g/kg), and OVX + 17beta-estradiol (4 mg/kg). OVX treatments reduced femoral and fourth lumbar vertebral bone density and mineral content (p<0.01), decreased uterine weight (p<0.01), accelerated body weight increases (p<0.05), and increased the activities (p<0.01) of both serum alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP). Supplementation with isoflavone prevented the losses of bone density and mineral content caused by OVX (p<0.01). Although both isoflavone and 17beta-estradiol exhibited similar bone-sparing ability on the OVX-induced bone loss, the effect of isoflavone was not the same as that of 17beta-estradiol on the serum ALP and TRAP, body weight increase, and uterine weight change. We concluded that dietary supplementation with soybean isoflavone can prevent postmenopausal bone loss via a different mechanism of estrogen in OVX rats.

Effects of exposure to genistein during pubertal development on the reproductive system of male mice.

Genistein, a soybean-originated isoflavone, is widely consumed by humans for putative beneficial health effects but its estrogenic activity may affect adversely the development of the male reproductive system. Twenty-one days old ICR mice weaned from dams fed with a casein-based AIN-76A diet during gestation and lactation were exposed to genistein (2.5 and 5.0 mg/kg/day, p.o.) for 5 weeks. 17beta-Estradiol (7.5 microg/kg/day) and corn oil were used for the positive and negative vehicle controls, respectively. The animals were fed the casein-based AIN-76A diet throughout the experiment. There were no significant differences in body weights of mice between the genistein groups and the negative control group. No significant differences in relative reproductive organ weights were found among all experimental groups. Sperm counts in epididymis and testes were slightly decreased in the genistein-exposed groups compared with control group. Sperm motile characteristics in genistein-exposed groups were slightly higher than those of the control group. Levels of phospholipid hydroxide glutathione peroxidase mRNA in the testis, epididymis, and prostate of mice exposed to genistein or estradiol were significantly higher than those of the controls (P<0.05). Exposure to genistein caused hyperplasia of Leydig cells in the testis and a slight increase of interstitial fibroblasts in the epididymis, while estradiol treatment caused severe damage to the testis and epididymis. These results suggest that dietary uptake of genistein during the juvenile period may affect male reproductive development, resulting in a slight decrease in sperm count, but with an increase in sperm motion quality.

Soy isoflavones improve spatial delayed matching-to-place performance and reduce cholinergic neuron loss in elderly male rats.

To investigate the protective activity of soy isoflavones on neurons, the effects of isoflavones on cholinergic enzyme activity, immunoreactivities of cholinergic enzyme, and delayed matching-to-place (DMP) performance were measured in normal elderly rats. Male Sprague-Dawley rats (n = 48; 10 mo old) were assigned to 3 groups: CD (control diet), ISO 0.3 (0.3 g/kg soy isoflavones diet), and ISO 1.2 (1.2 g/kg soy isoflavones diet). After 16 wk of consuming these diets, choline acetyltransferase (ChAT) activity in the ISO 0.3 group was greater in cortex and basal forebrain (BF; P < 0.05) than in controls. In BF, ChAT activity was also significantly greater in the ISO 1.2 group than in control rats. Acetylcholine esterase (AChE) activity in the ISO 0.3 group was significantly inhibited in cortex, BF, and hippocampus and in the ISO 1.2 group in cortex and hippocampus. Choline acetyltransferase immunoreactivity (ChAT-IR) in the ISO 1.2 group was significantly greater than in controls in the medial septum area. ChAT-IR in the ISO 0.3 and ISO 1.2 groups was significantly higher than in the CD group in the hippocampus CA1 area. Spatial DMP performance by the ISO 0.3 group showed significantly shorter swimming time than by the CD group. These findings show that soy isoflavones can influence the brain cholinergic system and reduce age-related neuron loss and cognition decline in male rats.