Short photoperiod restores ventral subicular lesion-induced deficits in affective and socio-cognitive behavior in male Wistar rats

Photoperiod (day-length) has enduring effects on an organism's physiological functions like metabolism and behavioral phenotypes including cognition and affect. Circadian rhythm manipulations are potentially effective non-pharmacological strategies in the management of central nervous system insults. In our previous study, we demonstrated the efficacy of short photoperiod regime (SPR; 06/18 hr light-dark cycle) in establishing functional recovery in ventral subicular lesion (VSL) rats. The present study further demonstrates the efficacy of SPR in mitigating anxiety and depression as well as facilitating socio-cognitive behavior in VSL rats. VSL elevated the basal plasma corticosterone levels, increased anxiety, anhedonia, and behavioral despair with decreased self-care. The VSL rats also exhibited a considerable degree of impaired social cognition, in terms of altered social preference and social novelty. Exposure to SPR for 21 days mitigated the anxiety- and depressive-like phenotypes as well as improved social cognition significantly. Thus, the study demonstrated the effectiveness of SPR strategy in reversing most of the behavioral deficits caused by VSL. SPR, perhaps, would have regulated the hypothalamo-pituitary-adrenal axis responsiveness as we observed a decrease in plasma corticosterone levels following SPR in VSL rats. The study implies the need for developing a task-dependent SPR strategy to achieve complete behavioral recovery as the functional demands of each behavior is distinct. In summary, the study highlights the efficacy of photoperiod manipulation as a novel, non-pharmacological approach in mitigating the affective and cognitive deficits associated with neuropsychiatric disorders such as bipolar disorder and Alzheimer's disease wherein circadian rhythm alterations are implicated.     

Temporal control of glucocorticoid neurodynamics and its relevance for brain homeostasis,neuropathology and glucocorticoid-based therapeutics

Glucocorticoids mediate plethora of actions throughout the human body. Within the brain, they modulate aspects of immune system and neuroinflammatory processes, interfere with cellular metabolism and viability, interact with systems of neurotransmission and regulate neural rhythms. The influence of glucocorticoids on memory and emotional behaviour is well known and there is increasing evidence for their involvement in many neuropsychiatric pathologies. These effects, which at times can be in opposing directions, depend not only on the concentration of glucocorticoids but also the duration of their presence, the temporal relationship between their fluctuations, the co-influence of other stimuli, and the overall state of brain activity. Moreover, they are region- and cell type-specific. The molecular basis of such diversity of effects lies on the orchestration of the spatiotemporal interplay between glucocorticoid- and mineralocorticoid receptors, and is achieved through complex dynamics, mainly mediated via the circadian and ultradian pattern of glucocorticoid secretion. More sophisticated methodologies are therefore required to better approach the study of these hormones and improve the effectiveness of glucocorticoid-based therapeutics.     

Withdrawal of repeated morphine enhances histamine-induced scratching responses in mice

An itch is experientially well known that the scratching response of conditions such as atopic dermatitis is enhanced under psychological stress. Morphine is typical narcotic drug that induces a scratching response upon local application as an adverse drug reaction. Although long-term treatment with morphine will cause tolerance and dependence, morphine withdrawal can cause psychologically and physiologically stressful changes in humans. In this study, we evaluated the effects of morphine withdrawal on histamine-induced scratching behavior in mice. Administration of morphine with progressively increasing doses (10–50?mg/kg, i.p.) was performed for 5 consecutive days. At 3, 24, 48, and 72?hr after spontaneous withdrawal from the final morphine dose, histamine was intradermally injected into the rostral part of the back and then the number of bouts of scratching in 60?min was recorded and summed. We found that at 24?hr after morphine withdrawal there was a significant increase in histamine-induced scratching behavior. The spinal c-Fos positive cells were also significantly increased. The relative adrenal weight increased and the relative thymus weight decreased, both significantly. Moreover, the plasma corticosterone levels changed in parallel with the number of scratching bouts. These results suggest that morphine withdrawal induces a stressed state and enhances in histamine-induced scratching behavior. Increased reaction against histamine in the cervical vertebrae will participate in this stress-induced itch enhancement.     

加味四逆散对青少期应激模型大鼠行为学和HPA轴的影响

目的:观察加味四逆散对青少期应激大鼠行为学、血浆促肾上腺皮质激素(ACTH)和血清皮质酮(CORT)浓度的影响。方法:32只SPF级雄性Wistar大鼠随机分为正常组,模型组,氟西汀组(0.01 g·kg~(-1)),加味四逆散组(16.9 g·kg~(-1)),采用慢性轻度不可预见性应激方法造模,造模同时ig给药28 d,每7 d称大鼠体重,检测糖水偏爱指数、旷场测试,采用放射免疫分析法检测大鼠血浆ACTH和血清CORT含量的改变。结果:与正常组比较,模型组大鼠出现体重增长缓慢、糖水偏爱指数明显降低,血浆ACTH和血清CORT含量明显升高(P0.05),而旷场测试大鼠的活跃度、总路程和平均速度均有所升高,中央区活动时间有所延长,但差异无统计学意义;与模型组比较,氟西汀组和加味四逆散组糖水偏爱指数明显升高(P0.05),血浆ACTH和血清CORT含量明显降低(P0.05),氟西汀组体重在第28天明显增加(P0.05)。结论:加味四逆散可以有效改善青少期应激大鼠行为学改变,下调其血浆ACTH和血清CORT含量,可能成为防治青少期应激损伤的有效方法。     

牛蒡子对运动训练大鼠睾酮及相关激素含量和抗运动疲劳能力的影响

目的:研究牛蒡子对运动训练大鼠睾酮及相关激素含量和抗疲劳能力的影响。方法:以大强度耐力训练大鼠为模型,55只42 d龄雄性Wistar大鼠为对象,随机分为5组:静止组(C组)、运动组(M组)、运动+低剂量牛蒡子组(AML组),运动+中剂量牛蒡子组(AMM组),运动+高剂量牛蒡子组(AMH组),每组10只(剔除不符合实验要求的大鼠5只)。每天灌胃ig给药1次,牛蒡子组剂量分为0.5,1,3 g·kg-1,ig体积为5 m L·kg-1,C,M组ig等量生理盐水。42 d力竭游泳训练后,测定体重、力竭游泳时间及血睾酮等生化指标。结果:体重,运动组小于静止组(P<0.05);牛蒡子各组>运动组(P<0.05)。力竭游泳时间,运动组与静止组无明显差异;牛蒡子各组明显长于运动组(P<0.01),且随剂量增大而延长。血清睾酮水平,运动组为(3.51±1.46)nmol·L-1低于静止组(P<0.01);牛蒡子低、中、高剂量组分别为(4.85±1.54),(4.97±1.47),(5.07±1.56)nmol·L-1,高于运动组(P<0.01)。血清皮质酮水平,各组间均无显著差异。血清睾酮与皮质酮比值变化与睾酮变化较为一致。血清促黄体生成素、促卵泡激素水平,静止组与运动组无显著差异;牛蒡子各组高于运动组(P<0.05)。结论:补充牛蒡子可以从多靶点、多途径纠正由于运动导致的下丘脑-垂体-性腺轴功能的紊乱,有效预防血清睾酮水平的降低,进而增强抗疲劳能力。     

亚麻籽对运动训练大鼠睾酮及相关激素含量和抗运动疲劳能力的影响

目的:研究亚麻籽对运动训练大鼠睾酮及相关激素含量和抗疲劳能力的影响。方法:以大强度耐力训练大鼠为模型,55只42 d龄雄性SPF级Wistar大鼠为对象,以数字随机分组法分为5组:静止组(C组)、运动组(M组)、运动+亚麻籽(FM)Ⅰ组(FMⅠ组),运动+亚麻籽Ⅱ组(FMⅡ组),运动+亚麻籽Ⅲ组(FMⅢ组),各组均为10只。每天ig 1次,亚麻籽组剂量分别为0.75,1.5,4.5 g·kg-1,ig体积为5 m L·kg-1,C,M组ig等量生理盐水。力竭游泳训练42 d后,分别测定各组大鼠体重、力竭游泳时间和血清睾酮等相关生化指标。结果:体重M组C组(P0.05);FM各组体重均M组(P0.05),且FM组间无显著差异。力竭游泳时间,M组与C组无明显差异;FM各组明显长于M组(P0.01)。血清睾酮水平,M组低于C组(P0.01);FM各组均高于M组(P0.01),分别为(4.83±1.15),(4.93±1.13),(5.11±1.12)nmol·L-1,且组间无显著差异。血清皮质酮水平,C,M,FM各组间无显著差异。血清睾酮与皮质酮比值变化与睾酮变化较为一致。血清促黄体生成素、促卵泡激素水平,C组高于M组,但无显著差异;FM各组高于M组(P0.05),且FM各组组间无显著差异。结论:补充亚麻籽可以纠正由于运动导致的下丘脑-垂体-性腺轴功能的紊乱,有效预防血清睾酮水平的降低,进而增强抗疲劳能力。     

Corticosterone analgesia is mediated by the spinal production of neuroactive metabolites that enhance GABAergic inhibitory transmission on dorsal horn rat neurons

Corticosterone (CORT) is a glucocorticoid produced by adrenal glands under the control of the hypothalamic–pituitary–adrenal axis. Circulating CORT can enter the central nervous system and be reduced to neuroactive 3α5α‐reduced steroids, which modulate GABA_A receptors. In the dorsal spinal cord, GABAergic transmission modulates integration of nociceptive information. It has been shown that enhancing spinal inhibitory transmission alleviates hyperalgesia and allodynia. Therefore, the spinal neuronal network is a pivotal target to counteract pain symptoms. Thus, any increase in spinal 3α5α‐reduced steroid production enhancing GABAergic inhibition should reduce nociceptive message integration and the pain response. Previously, it has been shown that high levels of plasma glucocorticoids give rise to analgesia. However, to our knowledge, nothing has been reported regarding direct non‐genomic modulation of neuronal spinal activity by peripheral CORT. In the present study, we used combined in vivo and in vitro electrophysiology approaches, associated with measurement of nociceptive mechanical sensitivity and plasma CORT level measurement, to assess the impact of circulating CORT on rat nociception. We showed that CORT plasma level elevation produced analgesia via a reduction in C‐fiber‐mediated spinal responses. In the spine, CORT is reduced to the neuroactive metabolite allotetrahydrodeoxycorticosterone, which specifically enhances lamina II GABAergic synaptic transmission. The main consequence is a reduction in lamina II network excitability, reflecting a selective decrease in the processing of nociceptive inputs. The depressed neuronal activity at the spinal level then, in turn, leads to weaker nociceptive message transmission to supraspinal structures and hence to alleviation of pain.     

Corticosterone and corticotropin‐releasing factor acutely facilitate gamma oscillations in the hippocampus in vitro

Stressful experiences do not only cause peripheral changes in stress hormone levels, but also affect central structures such as the hippocampus, implicated in spatial orientation, stress evaluation, and learning and memory. It has been suggested that formation of memory traces is dependent on hippocampal gamma oscillations observed during alert behaviour and rapid eye movement sleep. Furthermore, during quiescent behaviour, sharp wave‐ripple (SW‐R) activity emerges. These events provide a temporal window during which reactivation of memory ensembles occur. We hypothesized that stress‐responsive modulators, such as corticosterone (CORT), corticotropin‐releasing factor (CRF) and the neurosteroid 3α, 21‐dihydroxy‐5α‐pregnan‐20‐one (THDOC) are able to modulate gamma oscillations and SW‐Rs. Using in vitro hippocampal slices, we studied acute and subacute (2 h) impact of these agents on gamma oscillations in area cornu ammonis 3 of the ventral hippocampus induced by acetylcholine (10 μm ) combined with physostigmine (2 μm ). CORT increased the gamma oscillations in a dose‐dependent fashion. This effect was mediated by glucocorticoid receptors. Likewise, CRF augmented gamma oscillations via CRF type 1 receptor. Lastly, THDOC was found to diminish cholinergic gamma oscillations in a dose‐dependent manner. Neither CORT, CRF nor THDOC modulated gamma power when pre‐applied for 1 h, 2 h before the induction of gamma oscillations. Interestingly, stress‐related neuromodulators had rather mild effects on spontaneous SW‐R compared with their effects on gamma oscillations. These data suggest that the alteration of hippocampal gamma oscillation strength in vitro by stress‐related agents is an acute process, permitting fast adaptation to new attention‐requiring situations in vivo.     

Assessment of the involvement of the macrophage migration inhibitory factor–glucocorticoid regulatory dyad in the expression of matrix metalloproteinase‐2 during periodontitis

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine and counter‐regulator of endogenous glucocorticoids (GCs). It is implicated in acute and chronic inflammatory diseases. This study investigated the role of the MIF–GC regulatory dyad in the expression and release of matrix metalloproteinase‐2 (MMP‐2) during periodontitis, in vivo and in vitro. In a Mif‐knockout (KO) mouse model of ligature‐induced periodontitis, gingival tissues and blood were collected and analysed for levels of interleukin‐6 (IL‐6), MIF, MMP‐2, and corticosterone. In addition, human gingival fibroblasts (HGFs) were tested for production of IL‐6 and MMP‐2 after stimulation with hydrocortisone (HC), MIF, tumour necrosis factor‐alpha (TNF‐α), or Fusobacterium nucleatum, a pathogen known to elicit immune responses during periodontitis. Wild‐type (WT) mice showed a local and systemic increase of MIF levels during inflammation, which was confirmed by increased local IL‐6 concentrations. Systemic GC levels were reduced in WT and Mif‐KO mice during inflammation, with overall lower concentrations in Mif‐KO mice. In vivo and in vitro, MMP‐2 production was not dependent on MIF or inflammatory stimuli, but was inhibited by HC. Therefore, MIF does not appear to stimulate expression of MMP‐2 in the gingival tissues, whereas GC upregulates MIF and downregulates MMP‐2. Our findings further suggest that MIF may regulate systemic GC levels.