An intracerebroventricular injection of AΒ (1-42) modifies temporal profiles of spatial memory performance and oxidative status in the temporal cortex rat.

Alzheimer's dementia (AD) is a neurodegenerative disorder that causes memory loss and dementia in older adults. Intracellular accumulation of Aß causes an imbalance in the oxidative status and cognitive dysfunctions. Besides oxidative stress and loss of memory, Alzheimer's patients show dysfunction of the circadian rhythms. The objective of this work was to evaluate the consequences of an intracerebroventricular injection of Aß (1-42) on temporal patterns of cognitive performance, as well as on lipid peroxidation, protein oxidation and total antioxidant capacity levels, in the rat temporal cortex. Holtzman male rats from control and Aß-injected groups were used in this study. We found that MDA, protein carbonyls and total antioxidant capacity levels displayed day-night oscillations in the rat temporal cortex and spatial memory performance also varied rhythmically. An intracerebroventricular injection of Aß (1-42) modified temporal patterns of cognitive performance as well as daily profiles of parameters of oxidative stress. Thus, elevated levels of Aß aggregates induces alterations in daily rhythmicity of parameters of oxidative stress and, consequently, would affect cellular clock activity, affecting the spatial memory performance in the AD.

Daily rhythms in right-sided and left-sided temporal lobe epilepsy.

Introduction: Epilepsy is closely related to daily rhythms, such as the sleep-wake cycle. The objective of this study was to evaluate the relationship between drug-resistant temporal lobe epilepsy (TLE) and the parameters related to the sleep-wake cycle, seizure time and epilepsy laterality. Methods: Consecutive patients admitted to the video electroencephalogram unit with a diagnosis of TLE were enrolled. Patients were divided into two groups: those with left TLE (LTLE) and those with right TLE (RTLE). They then remained in the conditions of 12-hour light, 12-hour darkness. Demographic data, treatment, number and time of seizure occurrence, sleep diary, morningness-eveningness questionnaire, Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale were recorded. Results: In total, 74 patients with TLE, 43 with LTLE and 31 with RTLE, were studied. RTLE patients showed a significant preference for morningness. Patients treated with benzodiazepines showed worse sleep quality and greater daytime sleepiness. Patients who did not report any clear predominance and patients who reported seizures during wakefulness had significantly more seizures during wakefulness and patients who reported sleep predominance had more seizures during sleep (p>0.001). The LTLE group had a greater number of seizures from 8 to 16 hours, unlike the RTLE group, which had a uniform distribution (p=0.008). Conclusions: This was a prospective study of patients with drug-resistant TLE performed in a controlled environment to study the impact of daily rhythms, seizure frequency and seizure distribution. Laterality seems to be a key factor in seizure distribution.

Day-night oscillations of cognitive functions, TNF alpha and clock -related factors expression are modified by an intracerebroventricular injection of amyloid beta peptide in rat.

Alzheimer's disease (AD) is the most common form of dementia characterized by a gradual impairment in cognitive functions. Recent research have shown that TNF-α is a proinflammatory cytokine implicated in the pathogenesis of neurodegenerative diseases, such as AD. Besides cognitive deficit, AD patients show alterations in their circadian rhythms. The objective of this work was to investigate the effects of an intracerebroventricular injection of Aß aggregates on temporal patterns of cognitive functions and on daily rhythms of Aß, TNFα, BMAL1 and RORα protein levels in the rat prefrontal cortex. Four-month-old males Holtzman rats were used in this study. Groups were defined as: control and Aß-injected rats. Rats were maintained under 12h-light:12h-dark throughout the entire experimental period. Prefrontal cortex samples were isolated every 4 h during a 24h period. Our results demonstrated that an intracerebroventricular injection of Aß aggregates impaired learning and memory in rats at ZT 2 and ZT 14 and modified daily patterns of Aß, TNFα, and clock-related factors in the rat prefrontal cortex. Our findings showed that the increase of Aß altered temporal patterns of TNFα, and, consequently, induced alterations in daily rhythms of clock-related factors, affecting the cognitive performance of animals with Alzheimer's.

Aging disrupts the temporal organization of antioxidant defenses in the heart of male rats and phase shifts circadian rhythms of systolic blood pressure.

Aging is one of the main risk factors for cardiovascular diseases, and oxidative stress is a key element responsible for the development of age-related pathologies. In addition, the alteration of circadian rhythms also contributes to cardiovascular pathology, but the underlying mechanisms are not well defined. We investigated the aging consequences on the temporal patterns of antioxidant defenses, the molecular clock machinery, and the blood pressure, in the heart of male rats maintained under constant darkness (free running) conditions. Male Holtzman rats from young adult (3-month-old) and older (22-month-old) groups were maintained under constant darkness (12-h dark:12-h dark, DD) condition during fifteen days before the experiment. After the DD period, heart ventricle samples were isolated every 4-h throughout a 24-h period. We observed circadian rhythms of catalase (CAT) and glutathione peroxidase (GPx) mRNA expression, as well as ultradian rhythms of Nrf2 mRNA levels, in the heart of young adult rats. We also found circadian oscillations of CAT and GPx enzymatic activities, reduced glutathione (GSH) and BMAL1 protein in the same group. Interestingly, aging abolished the rhythms of CAT and GPx enzymatic activities, phase-shifted the rhythm's acrophases of GSH and BMAL1 protein levels and turned circadian the ultradian oscillation of Nrf2 expression. Moreover, aging phase-shifted the circadian pattern of systolic blood pressure. In conclusion, aging modifies the temporal organization of antioxidant defenses and blood pressure, probably, as a consequence of a disruption in the circadian rhythm of the clock's transcriptional regulator, BMAL1, in heart.

An intracerebroventricular injection of amyloid-beta peptide (1-42) aggregates modifies daily temporal organization of clock factors expression, protein carbonyls and antioxidant enzymes in the rat hippocampus.

Alzheimer disease (AD) is the most frequent form of dementia in the elderly. It is characterized by the deterioration of memory and learning. The histopathological hallmarks of AD include the presence of extracellular deposits of amyloid beta peptide, intracellular neurofibrillary tangles, neuron and synapse loss, in the brain, including the hippocampus. Accumulation of Aß peptide causes an increase in intracellular reactive oxygen species (ROS) and free radicals associated to a deficient antioxidant defense system. Besides oxidative stress and cognitive deficit, AD patients show alterations in their circadian rhythms. The objective of this work was to investigate the effects of an intracerebroventricular injection of amyloid beta peptide Aß(1-42) aggregates on temporal patterns of protein oxidation, antioxidant enzymes and clock factors in the rat hippocampus. Four-month-old male Holtzman rats divided into the groups control (CO) and Aß-injected (Aß), were maintained under 12 h-light12h-dark conditions and received water and food ad-libitum. Hippocampus samples were isolated every 6 h during a 24 h period. Our results showed daily patterns of protein carbonyls, catalase (CAT) and glutathione peroxidase (GPx) expression and activity, as well as Rorα and Rev-erbß mRNA, in the rat hippocampus. Interestingly, an intracerebroventricular injection of Aß aggregates modified daily oscillation of protein carbonyls levels, phase-shifted daily rhythms of clock genes and had a differential effect on the daily expression and activity of CAT and GPx. Thus, Aß aggregates might affect clock-mediated transcriptional regulation of antioxidant enzymes, by affecting the formation of BMAL1:CLOCK heterodimer, probably, as a consequence of the alteration of the redox state observed in rats injected with Aß.

Daily oscillation of cognitive factors is modified in the temporal cortex of an amyloid ß(1-42)-induced rat model of Alzheimer's disease.

Alzheimer's disease (AD) is a devastating disease characterized by loss of synapses and neurons in the elderly. Accumulation of the ß-amyloid peptide (Aß) in the brain is thought to be central to the pathogenesis of AD. ApoE plays a key role in normal and physiological clearance of Aß, since it facilitates the peptide intra- and extracellular proteolytic degradation. Besides the cognitive deficit, AD patients also show alterations in their circadian rhythms. The objective of this study was to investigate the effects of an i.c.v. injection of Aß (1-42) peptide on the 24 h rhythms of Apo E, BMAL1, RORα, Bdnf and trkB mRNA and Aß levels in the rat temporal cortex. We found that an i.c.v. injection of Aß aggregates phase shifts daily Bdnf expression as well as Apo E, BMAL1, RORα, Aß and decreased the mesor of TrkB rhythms. Thus, elevated Aß peptide levels might modify the temporal patterns of cognition-related factors, probably; by affecting the clock factors rhythms as well as in the 24 h rhythms of Apo E.

Effect of an Intracerebroventricular Injection of Aggregated Beta-amyloid (1-42) on Daily Rhythms of Oxidative Stress Parameters in the Prefrontal Cortex.

Accumulation of amyloid peptides in the brain plays a key role in the pathogenesis of Alzheimer's disease (AD). Aggregated beta-amyloid (Aß) peptide increases intracellular reactive oxygen species associated to a deficient antioxidant defense system. Prefrontal cortex plays a key role in memory and learning and is especially susceptible to oxidative stress. The objective of this work was to investigate the effects of an intracerebroventricular (i.c.v.) injection of Aß (1-42) on 24 h patterns of oxidative stress parameters and antioxidant defenses in the rat prefrontal cortex. Four-month-old male Holtzman rats were divided into two groups defined as: control (CO) and Aß-injected (Aß). Rats were maintained under12 h-light:12 h-dark conditions and received water and food ad libitum. Tissues samples were isolated every 6 h during a 24 h period. Interestingly, we found that an i.c.v. injection of Aß(1-42) increased lipid peroxidation, reduced total antioxidant capacity level, phase-shifted the daily peak of reduced glutathione, and had a differential effect on the oscillating catalase and glutathione peroxidase specific activity. Thus, elevated levels of Aß aggregates-a pathogenic hallmark of AD, caused altered temporal patterns of the cellular redox state in prefrontal cortex rat. These findings might contribute, at least in part, to the understanding of the molecular and biochemical basis of redox changes caused by circadian rhythms alterations observed in AD patients.

Effects of experimental intracerebral ventricular injection of amyloid beta peptide (1-42) aggregates on daily rhythms of Aß-degrading enzymes in the hippocampus: Relevance to Alzheimer's disease pathophysiology.

One of the main pathological features in the Alzheimer disease (AD) is the presence of senile plaques, primarily composed of Aß peptide aggregates, in cortex and hippocampus. AD late onset, which constitutes 90% of cases, could be mainly attributable to deficiencies in the clearance of the Aß peptide. Here we show that expression of Aß-degrading enzymes varies on a daily basis in the hippocampus. Interestingly, an intracerebroventricular injection of Aß aggregates modified temporal patterns of Aß-degrading proteases, as well as clock proteins (BMAL1 and RORα) and antioxidant enzymes (CAT and GPx) daily rhythms. Our findings showed that the increase of Aß leads to the alteration of the enzymes involved in the clearance, and, consequently, to an increase of oxidative stress and alteration of the cellular redox state, affecting the functioning of the endogenous clock and daily rhythms of BMAL1, RORα and their target genes, in this disease.

Peripheral Neuroimmunoendocrine Interactions: Contribution of TNFRp55 to the Circadian Synchronization of Progesterone and Cytokine Production in Joints of Mice in Late Pregnancy.

OBJECTIVE: Circadian rhythms are generated by the suprachiasmatic nucleus of the hypothalamus and involve rhythmic expression of clock genes and proteins. This rhythmicity is transferred to peripheral tissues by neural and hormonal signals. Late pregnancy is considered a state of inflammation which impacts on peripheral tissues such as joints. Tumor necrosis factor (TNF) mediates inflammatory and circadian responses through its p55 receptor (TNFRp55). Neuroimmunoendocrine interactions in joints have not been studied completely. The purpose of this study was to analyze these interactions, investigating the circadian rhythms of progesterone (Pg) and pro- and anti-inflammatory cytokines in the joints at the end of pregnancy (gestational day 18). Moreover, the impact of TNFRp55 deficiency on these temporal oscillations was explored. METHODS: Wild-type and TNFRp55-deficient (KO) C57BL/6 mice were kept under constant darkness in order to study their endogenous circadian rhythms. The expression of the clock genes Bmal1 and Per1 at circadian time 7 was studied by reverse transcription polymerase chain reaction in the ankle joints of nonpregnant and pregnant (gestational day 18) mice. In late pregnancy, Pg and the cytokines interleukin 17 (IL-17), IL-6, and IL-10 were measured in the joints throughout a 24-h period by radioimmunoassay and enzyme-linked immunosorbent assay, respectively. RESULTS: A significant increase in Bmal1 and Per1 mRNA expression was detected in the joints of pregnant KO mice. Furthermore, KO mice displayed a desynchronization of articular Pg and cytokine production. CONCLUSIONS: Our results show that TNF, via TNFRp55 signaling, modulates articular Pg and cytokine circadian rhythms in late pregnancy. These findings suggest a temporal neuroimmunoendocrine association in peripheral tissues in late pregnancy.

Circadian rhythms of factors involved in luteal regression are modified in p55 tumour necrosis factor receptor (TNFRp55)-deficient mice.

The rhythm of factors involved in luteal regression is crucial in determining the physiological duration of the oestrous cycle. Given the role of tumour necrosis factor (TNF)-α in luteal function and circadian regulation and that most of the effects of TNF-α are mediated by p55 TNF receptor (TNFRp55), the aims of the present study were to analyse the following during the luteal regression phase in the ovary of mice: (1) whether the pattern of expression of progesterone (P4) and the enzymes involved in the synthesis and degradation of P4 is circadian and endogenous (the rhythm persists in constant conditions, (i.e., constant darkness) with a period of about 24 hours); (2) circadian oscillations in clock gene expression; (3) whether there are daily variations in the expression of key genes involved in apoptosis and antioxidant mechanisms; and (4) the consequences of TNFRp55 deficiency. P4 was found to oscillate circadianally following endogenous rhythms of clock factors. Of note, TNFRp55 deficiency modified the circadian oscillation in P4 concentrations and its enzymes involved in the synthesis and degradation of P4, probably as a consequence of changes in the circadian oscillations of brain and muscle ARNT-Like protein 1 (Bmal1) and Cryptochrome 1 (Cry1). Furthermore, TNFRp55 deficiency modified the circadian rhythms of apoptosis genes, as well as antioxidant enzymes and peroxidation levels in the ovary in dioestrus. The findings of the present study strengthen the hypothesis that dysregulation of TNF-α signalling may be a potential cause for altered circadian and menstrual cycling in some gynaecological diseases.

Daily rhythms of cognition-related factors are modified in an experimental model of Alzheimer's disease.

The accumulation of amyloid-ß (Aß) peptides in the brain of Alzheimer disease patients is associated to cognitive deficit, increased oxidative stress, and alterations in the circadian rhythms. Brain-derived neurotrophic factor (BDNF) and Neurogranin (RC3), play an important role in the synaptic plasticity underlying memory and learning. Previously, we observed BDNF and RC3 expression follow a daily rhythmic pattern in the hippocampus of young rats. The objective of this study was to investigate the effects of an intracerebroventricular (i.c.v) injection of aggregated Aß peptide (1-42) on temporal patterns of ApoE protein, Bdnf and Rc3 mRNA, lipid peroxidation (LPO) and reduced glutathione (GSH) levels, in the rat hippocampus. We observed an i.c.v. injection of Aß aggregates phase shifts daily BDNF and RC3 expression as well as LPO and decreased the mesor of GSH rhythms. ApoE protein levels vary rhythmically throughout the day. ApoE levels increase at ZT 03:39±00:22 in the hippocampus of control rats and at ZT 06:30±00:28 in the treated animals. Thus, elevated levels of Aß aggregates, characteristic of AD, altered temporal patterns of cognition related-factors, probably, as a consequence of changes in the daily variation of ApoE-mediated Aß aggregates clearance as well as in the 24h rhythms of the cellular redox state.

Aging modifies daily variation of antioxidant enzymes and oxidative status in the hippocampus.

BACKGROUND: Aging is a complex and multifactorial biological process that leads to the progressive deterioration of physiological systems, including the circadian system. In addition, oxidative stress has been associated with the aging of the normal brain and the development of late-onset neurodegenerative diseases. Even though, functional weakening of circadian rhythms and antioxidant function has been observed during aging, the mechanisms by which the circadian system signaling and oxidative stress are interrelated have not yet been elucidated. The objectives of this study were to evaluate the consequences of aging on the temporal organization of the antioxidant defense system and oxidative status as well as to analyze the endogenous clock activity, in the hippocampus of aged rats. METHODS: Young adults (3-month-old) or older (22-month-old) male Holtzman rats were maintained under constant darkness conditions, during 15days before the sacrifice. Levels of catalase (CAT) and glutathione peroxidase (GPx) mRNA and activity, reduced glutathione (GSH), lipoperoxidation (LPO) and BMAL1 protein were analyzed in hippocampus samples isolated every 4h during a 24-h period. Locomotor activity was recorded during 20days before the experiment. RESULTS: Our results show that aging modifies temporal patterns of CAT and GPx expression and activity in the hippocampus in a different way. On the one hand, it abolishes the oscillating CAT expression and specific enzymatic activity while, on the other, it increases the mesor of circadian GPx activity rhythm (p<0.01). Additionally, we observed increased GSH (p<0.05) and reduced LPO (p<0.01) levels in the hippocampus of aged rats. Moreover, the nocturnal locomotor activity was reduced in the older animals in comparison to the young adult rats (p<0.01). Interestingly, the 22month-old animals became arrhythmic and showed a marked fragmentation as well as a significant decline in daily locomotor activity when they were maintained under constant darkness conditions (p<0.05). Aging also abolished circadian rhythms of the core clock BMAL1 protein. CONCLUSION: The loss of temporal organization of the antioxidant enzymes activity, the oxidative status and the cellular clock machinery could result in a temporally altered antioxidant defense system in the aging brain. Learning about how aging affects the circadian system and the expression of genes involved in the antioxidant defense system could contribute to the design of new strategies to improve the quality of life of older people and also to promote a healthy aging.

Rhythmic Bdnf and TrkB expression patterns in the prefrontal cortex are lost in aged rats.

Aging brain undergoes several changes leading to a decline in cognitive functions. Memory and learning-related genes such as Creb, Bdnf and its receptor TrkB, are expressed in different brain regions including prefrontal cortex. Those genes' proteins regulate a wide range of functions such as synaptic plasticity and long-term potentiation. In this work, our objectives were: 1) to investigate whether Creb1, Bdnf and TrkB genes display endogenous circadian expression rhythms, in the prefrontal cortex of rats maintained under constant darkness conditions; 2) to study the synchronization of those temporal patterns to the local cellular clock and 3) to evaluate the aging consequences on both cognition-related genes and activating clock transcription factor, BMAL1, rhythms. A bioinformatics analysis revealed clock-responsive (E-box) sites in regulatory regions of Creb1, Bdnf and TrkB genes. Additionally, cAMP response elements (CRE) were found in Bdnf and TrkB promoters. We observed those key cognition-related factors expression oscillates in the rat prefrontal cortex. Creb1 and TrkB mRNAs display a circadian rhythm with their highest levels occurring at the second half of the 24h period. Interestingly, the cosinor analysis revealed a 12-h rhythm of Bdnf transcript levels, with peaks occurring at the second half of the subjective day and night, respectively. As expected, the BMAL1 rhythm's acrophase precedes Creb1 and first Bdnf expression peaks. Noteworthy, Creb1, Bdnf and TrkB expression rhythms are lost in the prefrontal cortex of aged rats, probably, as consequence of the loss of BMAL1 protein circadian rhythm and altered function of the local cellular clock.

Participation of the extrinsic cholinergic innervation in the action of nitric oxide on the ovarian steroidogenesis in the first proestrous in rats.

An ex-vivo Coeliac Ganglion-Superior Ovarian Nerve-Ovary (CG-SON-O) system and an ovary without peripheral neural influence from virgin rats in the first proestrous were used to test whether ovarian extrinsic innervation and nitric oxide (NO) affects steroidogenesis in the ovary. The CG and the ovary were placed in separate buffered-compartments, connected by the SON. Stimulation of the CG was achieved by 10(-6)M acetylcholine (Ach). The ovary without peripheral neural influence was placed alone in a buffered-compartment. To test a possible role of NO in the ovarian response to peripheral neural influence, 100µM sodium nitroprusside (SNP, an NO donor) and 100µM N(G)-nitro-l-arginine methyl ester (l-NAME, an inhibitor of NO synthase) were added to the ovarian compartment separately. In the CG-SON-O system, SNP into the ovarian compartment increased the concentration of NO, reduced the release of progesterone and increased the release of estradiol (E2), increasing the mRNAs related to their synthesis enzyme. The addition of l-NAME to the ovarian compartment caused an opposite effect. In the ovary alone, NO manifested an antisteroidogenic effect on both hormones. These results show that the ovarian extrinsic innervation maintains a direct relationship between NO and E2, both needed at high levels during the follicular phase, allowing the continuity of the estrous cycle.

Oxidative stress and altered steroidogenesis in the ovary by cholinergic stimulation of coeliac ganglion in the first proestrous in rats. Implication of nitric oxide.

An ex-vivo Coeliac Ganglion-Superior Ovarian Nerve-Ovary (CG-SON-O) system from virgin rats in the first proestrous was used to test whether cholinergic stimulation of CG affects oxidative status and steroidogenesis in the ovary. The CG and the O were placed in separate buffered-compartments, connected by the SON, and the CG was stimulated by acetylcholine (Ach). To test a possible role of nitric oxide (NO) in the ovarian response to cholinergic stimulation of CG, aminoguanidine (AG) - an inhibitor of inducible-NO synthase was added to the O compartment. After 180 min incubation, the oxidative status was assessed in O whereas nitrite and steroidogenesis were assessed at 30, 120 and 180 min. Ach in CG decreased the total antioxidant capacity, but increased NO production and protein carbonization in O. Ach stimulation of CG increased estradiol, but decreased progesterone release in O by reducing the mRNAs related to their synthesis and degradation. The addition of AG to the O compartment caused an opposite effect, which was more pronounced in the presence of Ach in the CG compartment than in its absence. These results show that the stimulation of the extrinsic-cholinergic innervation of the O increases the concentration of NO, causes oxidative stress and modulates steroidogenesis in the first rat proestrous.

Circadian rhythms of locomotor activity and hippocampal clock genes expression are dampened in vitamin A-deficient rats.

The main external time giver is the day-night cycle; however, signals from feeding and the activity/rest cycles can entrain peripheral clocks, such as the hippocampus, in the absence of light. Knowing that vitamin A and its derivatives, the retinoids, may act as regulators of the endogenous clock activity, we hypothesized that the nutritional deficiency of vitamin A may influence the locomotor activity rhythm as well as the endogenous circadian patterns of clock genes in the rat hippocampus. Locomotor activity was recorded during the last week of the treatment period. Circadian rhythms of clock genes expression were analyzed by reverse transcription-polymerase chain reaction in hippocampus samples that were isolated every 4 hours during a 24-hour period. Reduced glutathione (GSH) levels were also determined by a kinetic assay. Regulatory regions of clock PER2, CRY1, and CRY2 genes were scanned for RXRE, RARE, and RORE sites. As expected, the locomotor activity pattern of rats shifted rightward under constant dark conditions. Clock genes expression and GSH levels displayed robust circadian oscillations in the rat hippocampus. We found RXRE and RORE sites on regulatory regions of clock genes. Vitamin A deficiency dampened rhythms of locomotor activity as well as modified endogenous rhythms of clock genes expression and GSH levels. Thus, vitamin A may have a role in endogenous clock functioning and participate in the circadian regulation of the cellular redox state in the hippocampus, a peripheral clock with relevant function in memory and learning.

Daily rhythms of catalase and glutathione peroxidase expression and activity are endogenously driven in the hippocampus and are modified by a vitamin A-free diet.

OBJECTIVES: Alterations in enzymatic antioxidant defense systems lead to a deficit of cognitive functions and altered hippocampal synaptic plasticity. The objectives of this study were to investigate endogenous rhythms of catalase (CAT) and glutathione peroxidase (GPx) expression and activity, as well as CREB1 mRNA, in the rat hippocampus, and to evaluate to which extent the vitamin A deficiency could affect those temporal patterns. METHODS: Rats from control and vitamin A-deficient (VAD) groups received a diet containing 4000 IU of vitamin A/kg diet, or the same diet devoid of vitamin A, respectively, during 3 months. Rats were maintained under 12-hour-dark conditions, during 10 days before the sacrifice. Circadian rhythms of CAT, GPx, RXRγ, and CREB1 mRNA levels were determined by reverse transcriptrase polymerase chain reaction in hippocampus samples isolated every 4 hours during a 24-hour period. CAT and GPx enzymatic activities were also determined by kinetic assays. Regulatory regions of clock and antioxidant enzymes genes were scanned for E-box, RXRE, and CRE sites. RESULTS: E-box, RXRE, and CRE sites were found on regulatory regions of GPx and CAT genes, which display a circadian expression in the rat hippocampus. VAD phase shifted CAT, GPx, and RXRγ endogenous rhythms without affecting circadian expression of CREB1. DISCUSSION: CAT and GPx expression and enzymatic activity are circadian in the rat hippocampus. The VAD affected the temporal patterns antioxidant genes expression, probably by altering circadian rhythms of its RXR receptors and clock factors; thus, it would impair the temporal orchestration of hippocampal daily cognitive performance.

Retinoic acid receptors move in time with the clock in the hippocampus. Effect of a vitamin-A-deficient diet.

An endogenous time-keeping mechanism controls circadian biological rhythms in mammals. Previously, we showed that vitamin A deficiency modifies clock BMAL1 and PER1 as well as BDNF and neurogranin daily rhythmicity in the rat hippocampus when animals are maintained under 12-h-light:12-h-dark conditions. Retinoic acid nuclear receptors, retinoic acid receptors (RARs) and retinoid X receptors (RXRs), have been detected in the same brain area. Our objectives were (a) to analyze whether RARα, RARß and RXRß exhibit a circadian variation in the rat hippocampus and (b) to investigate the effect of a vitamin-A-deficient diet on the circadian expression of BMAL1, PER1 and retinoic acid receptors (RARs and RXRß) genes. Holtzman male rats from control and vitamin-A-deficient groups were maintained under 12-h-light:12-h-dark or 12-h-dark:12-h-dark conditions during the last week of treatment. RARα, RARß, RXRß, BMAL1 and PER1 transcript and protein levels were determined in hippocampus samples isolated every 4 h in a 24-h period. Regulatory regions of RARs and RXRß genes were scanned for clock-responsive sites, while BMAL1 and PER1 promoters were analyzed for retinoic acid responsive elements and retinoid X responsive elements. E-box and retinoid-related orphan receptor responsive element sites were found on regulatory regions of retinoid receptors genes, which display an endogenously controlled circadian expression in the rat hippocampus. Those temporal profiles were modified when animals were fed with a vitamin-A-deficient diet. Similarly, the nutritional vitamin A deficiency phase shifted BMAL1 and abolished PER1 circadian expression at both mRNA and protein levels. Our data suggest that vitamin A deficiency may affect the circadian expression in the hippocampus by modifying the rhythmic profiles of retinoic acid receptors.

Daily oscillation of glutathione redox cycle is dampened in the nutritional vitamin A deficiency.

Examples of hormonal phase-shifting of circadian gene expression began to emerge a few years ago. Vitamin A fulfills a hormonal function by binding of retinoic acid to its nuclear receptors, RARs and RXRs. We found retinoid- as well as clock-responsive sites on regulatory regions of Glutathione reductase (GR) and Glutathione peroxidase (GPx) genes. Interestingly, we observed retinoid receptors, as well as GSH, GR and GPx, display daily oscillating patterns in the rat liver. We also found that feeding animals with a vitamin A-free diet, dampened daily rhythms of RARα and RXRß mRNA, GR expression and activity, GSH, BMAL1 protein levels and locomotor activity. Differently, day-night oscillations of RXRα, GPx mRNA levels and activity and PER1 protein levels, were phase-shifted in the liver of vitamin A-deficient rats. These observations would emphasize the importance of micronutrient vitamin A in the modulation of biological rhythms of GSH and cellular redox state in liver.