大鼠下丘脑弓状核突触的衰老性变化

用透射电镜结合体视学方法，对３月龄、１０月龄和３０～３４月龄大鼠弓状核突触进行了定性和定量研究。结果显示：老龄组大鼠神经毯呈萎缩变性相，大树突内脂褐素增多，小到中等大小的树突出现空泡变性、多泡体和膜被多层体等，棘萎缩减少；轴突终末内突触囊泡减少而大颗粒囊泡积聚，部分突触前、后膜变薄、缩短或间断，突触小球少见；轴－体、轴－树和轴－棘突触数减少，突触密度、突触连接带面密度和突触膜总长度降低，ＧｒａｙⅠ型和即Ⅱ型突触间隙增宽。上述结果表明，老年弓状核突触在数量、形态和结构上发生了衰老性改变，这是导致下丘脑神经内分泌衰老障碍的主要原因之一。     

Effect of estrogen of early postnatal development of synaptic formation in the hypothalamic arcuate nucleus of female rats

Female rats were given injections of estradiol benzoate for the first 30 days of their postnatal life; i.e., 2 μg for the first 10 days and 4 μg and 8 μg for the middle and last 10 days, respectively. On the day following the last injection (31 days of age), the hypothalamic arcuate nucleus (ARCN) was examined ultrastructurally and the axodendritic and axosomatic synapses were counted in a field of 10,117.5 μm² in the middle part of the ARCN. The mean number of axodendritic synapses in the ARCN of the neonatally estrogenized females was about two-fold greater than that of oil-treated controls. As for the number of axosomatic synapses, of which incidence was low, there was no significant difference between the estrogenized and control animals. From these results it is suggested that an increase in the number of axodendritic synapses in the ARCN is caused by neonatal treatment with estrogen.     

大鼠下丘脑弓状核神经元的衰老性变化

选用青、中年和老年雄性大鼠各１０只，用形态计量学和体视学方法定量分析弓状核神经元年龄性变化。结果发现在老年大鼠弓状核，部分暗型和亮型神经元内粗面内质网排列紊乱、缩短和双层膜间隔增宽，线粒体嵴断裂、肿胀和空泡化，溶酶体，微管和颗粒小泡数减少；与青、中年组比较神经元数分别丢失３７％和２７％，核仁平均体积缩小３０％左右；     

Age-dependent effects of deafferentation of the rat superior cervical ganglion on expression of P65 (synaptotagmin) during postnatal development.

Previous studies have shown that deafferentation of the rat superior cervical ganglion (SCG) alters the levels of p65 (synaptotagmin), a synaptic vesicle integral membrane protein, within the ganglion. Neonatal deafferentation blocks normal postnatal increases in p65, while deafferentation in adult animals produces a transient increase in p65 expression. The present study examines the time course of the shift from the neonatal to adult pattern of response to deafferentation. Neonatal and 7 day old rats showed the neonatal response to deafferentation. Ganglia from rats aged 14 days or older at deafferentation exhibited the transient increase in p65 at 7 days after surgery. The shift from the neonatal to adult response occurs during the second postnatal week. The change in response to deafferentation may be associated with refinement of synaptic function in a manner yet to be determined.     

Medial preoptic islands in the rat brain: electron microscopic evidence for intrinsic synapses

Summary Neurons intrinsic to the preoptic area might participate in the control of neuroendocrine or behavioral events. To determine their existence and features, we deafferented the preoptic area of female rats, using completely circumscribing cuts with a Halasz knife. Despite obvious signs of degeneration of synapses originating from nerve cell bodies outside the preoptic island, some synapses survived complete deafferentation. We saw synaptic contacts not only on the neuronal cell body, but also on the dendritic shaft and spine. There were no peculiar morphological features, as might suggest unique physiologic functions of these intrinsic synapses. The prominence of intrinsic synapses in the preoptic area suggests that, in addition to hormone effects on preoptic neurons, and long ascending afferents, intrinsic synapses might play significant roles in neuroendocrine controls.     

Recovery of lordotic activity by dorsal deafferentation of the preoptic area in male and androgenized female rats

Lordotic activity was examined in male and neonatally androgenized female rats following dorsal deafferentation of the preoptic area (POA). Female pups were injected with various doses (100, 250, 500, or 1000 micrograms) of testosterone propionate (TP) on day 3 postpartum. Ten weeks after birth, all animals were castrated, then half of the castrated males and females in each group were subjected to dorsal deafferentation of the POA (anterior roof deafferentation: ARD) by using an L-shaped Halász knife in order to transect the dorsal forebrain efferents which are thought to exert an inhibitory influence on the lordosis mediating mechanism. Animals were implanted subcutaneously with Silastic tubes containing estradiol-17 beta (E2). Observations of lordosis behavior were carried out 5, 10, and 15 days after implantation of E2. Three to six hours before each behavioral test, all rats were injected with 0.5 mg progesterone. Regardless of the dose of TP given neonatally, androgenized females, as well as males, showed low levels of lordotic behavior. In contrast, males with ARD and androgenized females with ARD displayed lordosis more frequently than males without ARD, and androgenized females without ARD. Lordotic activity in the androgenized females with ARD was negatively correlated with the dose of TP given neonatally. The ARD females injected with a large dose (1000 micrograms) of TP neonatally were significantly less receptive than those injected with lower doses of TP and ARD males. These results suggest that a large dose of neonatal TP may cause permanent changes in not only the neural substrates for lordosis inhibition affected by ARD but also other structures involved in lordosis facilitation.     

Estrogen and aging affect synaptic distribution of phosphorylated LIM kinase (pLIMK) in CA1 region of female rat hippocampus

17beta-Estradiol (E) increases axospinous synapse density in the hippocampal CA1 region of young female rats, but not in aged rats. This may be linked to age-related alterations in signaling pathways activated by synaptic estrogen receptor alpha (ER-alpha) that potentially regulate spine formation, such as LIM-kinase (LIMK), an actin depolymerizing factor/cofilin kinase. We hypothesized that, as with ER-alpha, phospho-LIM-kinase (pLIMK) may be less abundant or responsive to E in CA1 synapses of aged female rats. To address this, cellular and subcellular distribution of pLIMK-immunoreactivity (IR) in CA1 was analyzed by light and electron microscopy in young and aged female rats that were ovariectomized and treated with either vehicle or E. pLIMK-IR was found primarily in perikarya within the pyramidal cell layer and dendritic shafts and spines in stratum radiatum (SR). While pLIMK-IR was occasionally present in terminals, post-embedding quantitative analysis of SR showed that pLIMK had a predominant post-synaptic localization and was preferentially localized within the postsynaptic density (PSD). The percentage of pLIMK-labeled synapses increased (30%) with E treatment (P<0.02) in young animals, and decreased (43%) with age (P<0.002) regardless of treatment. The pattern of distribution of pLIMK-IR within dendritic spines and synapses was unaffected by age or E treatment, with the exception of an E-induced increase in the non-synaptic core of spines in young females. These data suggest that age-related synaptic alterations similar to those seen with ER-alpha occur with signaling molecules such as pLIMK, and support the hypothesis that age-related failure of E treatment to increase synapse number in CA1 may be due to changes in the molecular profile of axospinous synapses with respect to signaling pathways linked to formation of additional spines and synapses in response to E.     

Neural transection between preoptic area and septum inhibits maternal behavior in female and male rats

Artificially-induced maternal behavior was examined in inexperienced female and male rats following neural transection between the preoptic area and the septum. Anterior roof deafferentation (ARD) of the preoptic area (POA) was performed with an L-shaped microknife. Virgin female and male rats with or without ARD were exposed to the continuous presence of normal pups to induce maternal behavior 3 weeks after surgery. ARD resulted in a significant delay of the onset of maternal behavior in females and a lack of complete development of maternal behavior in males, compared with corresponding sham-operated and intact controls. The results indicate that neural substrates dorsal to the POA play an important role in modulating the expression of maternal behavior in the rat.     

Bone loss in regucalcin transgenic rats: enhancement of osteoclastic cell formation from bone marrow of rats with increasing age

Bone loss was previously shown to be induced in the femoral tissue of regucalcin transgenic (TG) rats. Regucalcin is expressed in rat bone marrow cells and its expression is enhanced in regucalcin TG rats. This study was undertaken to determine the change in osteoclastic bone resorption in regucalcin TG rats with increasing age. Femoral-diaphyseal and -metaphyseal tissues were obtained from normal (wild-type) and regucalcin TG rats aged 5, 14, 25 or 50 weeks. Calcium content in the femoral-diaphyseal and -metaphyseal tissues was significantly decreased in regucalcin TG male and female rats aged 5, 14, 25 or 50 weeks as compared with the value obtained from normal rats with each age. When the marrow cells obtained from normal or regucalcin TG rats were cultured for 7 days, the number of tartrate-resistant acid phosphatase (TRACP), a marker of osteoclasts, positive multinucleated cells (MNCs) were significantly increased in the marrow culture of regucalcin TG male and female rats aged 5, 14, 25 or 50 weeks. The effect of parathyroid hormone [human PTH (1-34); 10(-7) M] or 1,25-dihydroxyvitamin D3 [1,25(OH)2D3; 10(-7) M] in stimulating TRACP-positive MNC formation was significantly enhanced in regucalcin TG male and female rats aged 14 or 25 weeks. This study demonstrates that osteoclastic bone resorption is stimulated in regucalcin TG male and female rats with increasing age.     

Age-related attenuation of stimulated cortical acetylcholine release in basal forebrain-lesioned rats

In vivo microdialysis was used to measure the effects of partial deafferentation of cortical cholinergic inputs on acetylcholine efflux in young (four to seven months) and aged (24-28 months) male F344/BNNIA rats. Partial deafferentation was produced by bilateral infusions of the immunotoxin 192 immunoglobulin G-saporin (0.56 microg/1.0 microl) or its vehicle solution into the ventral pallidum/substantia innominata region of the basal forebrain. The lesion produced comparable (65%) decreases in basal cortical acetylcholine efflux in young and aged rats. Presentation of a complex environmental stimulus (exposure to darkness/palatable food), in conjunction with the systemic administration of the benzodiazepine receptor weak inverse agonist ZK 93 426, increased cortical acetylcholine efflux in young shams, aged shams and young lesioned rats, but not in aged lesioned rats. Administration of the benzodiazepine receptor partial inverse agonist FG 7142, in the absence of the environmental stimulus, comparably stimulated cortical acetylcholine efflux in young and aged sham rats. FG 7142-induced increases in acetylcholine efflux were attenuated by approximately 50% following partial deafferentation in both young and aged rats. These results suggests that, under certain conditions, ageing potently interacts with the integrity of the cortical cholinergic afferent system. The effects of ageing on cortical cholinergic function may be most potently revealed by experiments assessing age-related limitations in the responsiveness of a partially deafferented cholinergic system to certain behavioral and/or pharmacological stimuli.     

Synaptic strength and postsynaptically silent synapses through advanced aging in rat hippocampal CA1 pyramidal neurons

Synaptic dysfunction is thought to contribute to age-related learning impairments. Detailed information regarding the presence of silent synapses and the strength of functional ones through advanced aging, however, is lacking. Here we used paired-pulse minimal stimulation techniques in CA1 stratum radiatum to determine whether the amplitude of spontaneous and evoked miniature excitatory postsynaptic currents (sEPSCs and eEPSCs, respectively) changes over the lifespan of rats in hippocampal CA1 pyramidal neurons, and whether silent synapses are present in adult and aged rats. The amplitudes of both sEPSCs and eEPSCs at resting membrane potential (i.e., clamped at -65 mV) initially increased between 2 weeks and 3 months, but then remained constant through 36 months of age. The potency of the eEPSCs at depolarized membrane potentials (i.e., clamped at +40 mV), however, was highest among 36-month old rats. Additionally, presynaptically silent synapses in CA1 stratum radiatum disappeared between 2 weeks and 3 months, but postsynaptically silent synapses were present through advanced aging. The similarity of silent and functional synapses in CA1 hippocampus at resting membrane potentials throughout adulthood in rats may indicate that impairments in the mechanisms of synaptic plasticity and its subsequent stabilization, rather than deficient synaptic transmission, underlie age-related cognitive decline. Such a notion is consistent with the increased amplitude of synaptic currents at depolarized potentials, perhaps suggesting an upregulation in the expression of synaptic NMDA receptors once rats reach advanced age.     

Changes in expression of a synaptic vesicle antigen in aging sympathetic neurons

The effects of altering synaptic activity of sympathetic neurons on the expression of a synaptic vesicle protein (p65) were studied by deafferentation of the superior cervical ganglion (SCG) in adult and aged Fischer-344 rats. Levels of p65, an integral membrane protein of synaptic vesicles, were assayed by radioimmunoassay. After deafferentation, a transient increase in p65 levels is observed in the SCG of adult rats. In aged animals, the response to deafferentation is delayed and enhanced, and levels do not drop to values observed in operated adults. After SCG deafferentation, p65 levels in the iris, an SCG target, initially are depressed below control levels; p65 levels return to control values in adult animals after 14 days, but remain depressed in aged animals. In contrast, a transient increase in p65 levels is observed in the pineal of both adult and aged animals. These results suggest that while the aged sympathetic nervous system retains the ability to respond to alterations in synaptic activity, it is unable to reregulate once a response is initiated.     

Synapse formation occurs in association with the induction of long-term potentiation in two-year-old rat hippocampus in vitro.

Following induction of long-term potentiation in subfield CA1 of the hippocampal slice from 26-month-old rats, shaft synapse numbers increased by 44% and sessile spine synapses (synapses on stubby, headless spines) by 72%, with the more common mushroom-shaped spine synapses statistically unaltered. These effects are smaller than in prior work with young adults, whereas population spike amplitude changes were comparable to young adults. Reasons for the discrepancy are unclear, but the results confirm continuing capacity for induction of LTP in aged rats and indicate that substantial synaptogenic capacity also persists, but may be impaired, at these ages.     

Serum amyloid P component regulation by sex steroids in rats

Serum amyloid P component (SAP) has been designated as a female protein in hamsters. To investigate the effects of sex steroids on SAP concentration in rats, SAP was purified from Wistar rats by affinity chromatography. Anti-SAP was raised. Sample sera were obtained from 150 young and old rats, after which, they were injected with either estradiol (E2), testosterone (T), or dehydroepiandrosterone (DHA). Sera were serially obtained from the tail vessels until the 8th day after injection. Serum levels of SAP were measured by micro single radial immuno-diffusion with a standard pooled serum as 100%. As the rats aged, the SAP levels in untreated female rats increase with age from 93% at 11 weeks to 346% at 58 weeks. In 28-week-old rats, the SAP levels in females (135 +/- 40%) were significantly (p less than 0.01) higher than those in males (80 +/- 32%). When old female rats (56 wk) were injected with DHA (3.5 mg), the SAP decreased significantly (p less than 0.01) to 70.8% of the preinjection level on the 8th day after injection. When young male rats (11 wk) were jnjected with E2 (0.5 mg), the SAP levels increased rapidly to 188% of the prelevel on the 5th day. Serum E2 levels reached a peak on the 2nd day. After the injection of T, the SAP levels did not change.     

Changes in hippocampal synapses and learning-memory abilities in age-increasing rats and effects of tetrahydroxystilbene glucoside in aged rats

The aim of the present study is to investigate the changes in hippocampal synapses and their relation with learning-memory abilities at different ages, and evaluate the effects of 2,3,5,4'-tetrahydroxystilbene-2-O-beta-d-glucoside (TSG), which is one of the major components of a traditional Chinese herb Polygonum multiflorum, on brain aging. Sprague-Dawley rats at the age of 1, 3, 6, 18 and 24 months were used. TSG at doses of 30 and 60 mg/kg/day was intragastrically administered to 21-month-old rats for 3 months, respectively. Learning-memory abilities were determined by Morris water maze and passageway water maze tests. The ultrastructure of synapses in the hippocampal CA1 region was observed by electronic microscopy. The expression of synaptophysin (SYP) in whole hippocampus was measured by using immunohistochemistry. Compared with rats at 6 months of age, both the 1-month-old rats and 24-month-old rats showed longer escape latency and swimming distance in the Morris water maze test, while more errors were detected in the passageway water maze test, with a smaller number of synapses and synaptic vesicles and less expression of SYP in the hippocampus. Treatment with high-dose TSG in rats at 24 months of age had significant improvement in the learning-memory abilities in the water maze tests associated with an increase in the number of synapses and synaptic vesicles, and an elevation of expression of SYP in the hippocampus. In conclusion, hippocampal synapses count and synaptophysin expression decreased in aged rats, which may be one of the mechanisms involved in learning-memory deficit. TSG reversed the above changes in aged rats, suggesting that TSG may be beneficial for the treatment of Alzheimer disease or cognitive impairment in old people.     

Early lesion of mystacial vibrissae in rats results in an increase of somatostatin-labelled cells in the somatosensory cortex

Summary Recent studies in the developing cortex have shown that during the first 2 postnatal weeks somatostatin (SRIF)-containing neurons appear in greater numbers. After this time their numbers decline significantly probably due to cell death (Cavanagh and Parnavelas 1988). In this study we report changes in the distribution of SRIF-labelled cells in the somatosensory cortex of adult rats following unilateral lesions of mystacial vibrissae at birth. Specifically, we observed that the side contralateral to the lesion contained a significantly greater number of labelled cells compared to the ipsilateral side. We suggest that the decline in cell numbers observed during normal development is reduced following early deafferentation.     

Age, sex and strain comparison of habituation of the startle response in the rat

Habituation and sensitization of the acoustic startle response were studied in young (3 month) and aged (26 month) male and female Fischer 344 rats and in young (3 month) and aged (32 month) male Sprague Dawley rats. Tones were presented on 25 consecutive trials for a session, one session on each of four consecutive days. An air puff stimulus immediately preceded trial 20 on each day to test sensitization. All aged rats demonstrated greater short-term (within session) relative habituation than their younger counterparts. Across sessions, aged male rats of both strains habituated more quickly than younger males. Aged female rats habituated more slowly. Sensitization was more likely to occur in younger rats.     

吗啡依赖对大鼠生理性依赖相关脑区突触数量的影响

目的：观察不同时程吗啡依赖大鼠生理性依赖相关脑区突触数量的变化。方法：背部皮下递增注射吗啡建立不同时程吗啡依赖大鼠模型，应用透射电镜对吗啡依赖鼠生理性依赖相关脑区蓝斑核、中脑导水管周围灰质、黑质突触进行观察计数，并与空白对照组进行比较。结果：吗啡依赖大鼠蓝斑核、中脑导水管周围灰质、黑质突触数量增多；吗啡依赖8w组、吗啡依赖4w组大鼠突触数量的增多与空白对照组大鼠相比，具有高度显著性差异；吗啡依赖8w组大鼠突触数量的增多与吗啡依赖1w组、吗啡依赖2w组大鼠相比，具有显著性差异。结论：吗啡依赖大鼠生理性依赖相关脑区突触数量增多，并随吗啡依赖时限的延长而更加明显。     

Deficits in nitric oxide production after tetanic stimulation are related to the reduction of long-term potentiation in Schaffer-CA1 synapses in aged Fischer 344 rats

In the present study, we investigated whether nitric oxide (NO) production after tetanic stimulation is involved in long-term potentiation (LTP) in Schaffer-CA1 synapses in both young adult and aged rats. The changes in both the population spike amplitude and NO metabolites, nitrite (NO2-) and nitrate (NO3-), in the CA1 region were simultaneously determined before and after tetanic stimulation. Increases in NOx (NO2- plus NO3-) levels in the CA1 region were observed after tetanic stimulation in young adult rats as well as increase in the population spike amplitude. In aged rats, LTP was significantly inhibited compared with that in young adult rats. No increase in NOx level after tetanic stimulation was observed in aged rats. These findings directly demonstrated that NO production might be involved in the process of LTP formation in Schaffer-CA1 synapses of the rat hippocampus, and that the deficiency of hippocampal NO production might be responsible for reduction of LTP formation in aged rats.     

Synaptic remodelling and astrocytic hypertrophy in rat cerebral cortex from early to late adulthood

Ultrastructural observation of the molecular layer of the parietal cortex of rats, aged 3, 6, 10 and 17 months, revealed various atypical synaptic profiles besides typical synapses. The atypical synapses were frequently in the vacinity of hypertrophied astrocytic profiles, and were sometimes completely surrounded by astrocytic processes. The presynaptic terminal contained either no vesicles or a few small distored vesicles. Vacant postynaptic terminals were occasionally seen. The total surface area of astrocytic profiles and the numbers of atypical synapses increased significantly between 3 and 10 months. The astrocytic acquistion of degerating terminals was repeatedly observed over this period. Since there was no decrease in total synaptic number at this age, the astrocytic phenomenon may represent a stage in a continuous cycle of synaptic loss and replacement in the normal brain. By 17 months, when total synapse numbers decrease, synaptic replacement may be less than optimal.