Cerebral Inositol Research Articles

Digital Gene Expression Profiling reveals transcriptional responses to acute cold stress in Chinese soft-shelled turtle Pelodiscus sinensis juveniles

Turtles are well known for their stress tolerance, including an ability to deal with temperature extremes or rapid thermal change. To know more about the comprehensive molecular basis of thermal stress responses in turtles, we assessed differentially expressed genes (DEGs) in the brain, liver and kidney of juvenile soft-shelled turtles, Pelodiscus sinensis, after acute cold stress (28 °C–8 °C acute transfer and held for 12 h) and following recovery (back to 28 °C and held for 24 h) by digital gene expression profiling. Selected DEGs were also validated via real-time PCR. We found the fewest DEGs in the brain, only one-tenth of the number seen in liver, indicating a tissue-specific gene expression pattern. The DEGs indicated the potential activation of several important functions in response to cold stress and recovery in P. sinensis. This included response to oxidative stress or regulation of reactive oxygen species metabolism in the brain and liver, cerebral inositol metabolism, hepatic monosaccharide metabolism, hepatic complement system, renal DNA repair mechanisms, and TNF and PI3K-Akt signaling pathways in the kidney. These functions likely responded to cold stress in different tissues of P. sinensis to help minimize or repair cell damage as well as enhance innate immunity. The outcomes of this study provide some fundamental insight into the tissue specific complex mechanisms underlining cold stress responses in the soft-shelled turtle P. sinensis.

Brain metabolism in Alzheimer disease and vascular dementia assessed by in vivo proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy (MRS) allows the assessment of various cerebral metabolites non-invasively in vivo. Among 1H MRS-detectable metabolites, N-acetyl-aspartate and N-acetyl-aspartyl-glutamate (tNAA), trimethylamines (TMA), creatine and creatine phosphate (tCr), inositol (Ins) and glutamate (Gla) are of particular interest, since these moieties can be assigned to specific neuronal and glial metabolic pathways, membrane constituents, and energy metabolism. In this study on 94 subjects from a memory clinic population, 1H MRS results (single voxel STEAM: TE 20 ms, TR 1500 ms) on the above metabolites were assessed for five different brain regions in probable vascular dementia (VD), probable Alzheimer's disease (AD), and age-matched healthy controls. In both VD and AD, ratios of tNAA/tCr were decreased, which may be attributed to neuronal atrophy and loss, and Ins/tCr-ratios were increased indicating either enhanced gliosis or alteration of the cerebral inositol metabolism. However, the topographical distribution of the metabolic alterations in both diseases differed, revealing a temporoparietal pattern for AD and a global, subcortically pronounced pattern for VD. Furthermore, patients suffering from vascular dementia (VD) had remarkably enhanced TMA/tCr ratios, potentially due to ongoing degradation of myelin. Thus, the metabolic alterations obtained by 1H MRS in vivo allow insights into the pathophysiology of the different dementias and may be useful for diagnostic classification.

Sustained Effects of Pilocarpine-Induced Convulsions on Brain Inositol and Inositol Monophosphate Levels and Brain Morphology in Young and Old Male Rats

Cerebral inositol and inositol monophosphates, products of phosphoinositide (PI) turnover, and neuronal injury were studied in young (10 weeks) and old (24 months) male Wistar rats after pilocarpine-induced convulsions. The goal was to explore the association between short-term cholinergic convulsions, brain PI signaling, and changes in the brain morphology in the young and the old rats. Pilocarpine caused convulsions in young rats at a dose of 300 mg/kg, whereas a dose of 175 mg/kg was required to obtain the same effect in old rats. A dose of 5 mg/kg of diazepam was used to terminate the convulsions 2 hr after their initiation; the rats were then examined on Day 5 postpilocarpine. Inositol and inositol monophosphate levels were similar in both the young and the old control rats. Pilocarpine-induced convulsions decreased cerebral inositol and increased inositol-1-phosphate in both the young and the old rats. Inositol-4-phosphate was stable in the young rats but increased in the frontal cortex and the hippocampus in the old rats. Delayed neuronal death also occurred in the convulsing rats, i.e., a variable proportion of neurons appeared shrunken with eosinophilic cytoplasm and pyknotic nuclei. The hippocampus was the most severely affected brain area. These results show that old rats are more sensitive than young ones to short-term pilocarpine convulsions, associated with sustained PI turnover, and brain injury. Mechanisms in addition to cholinergic ones are likely to be involved in the prolonged cerebral effects of cholinergic convulsions in rats.

Malaoxon-induced neurotoxicity in old rats: alterations in cerebral inositol lipid signalling, brain tissue calcium levels and early neuronal injury

Effects of malaoxon (MO) on brain regional inositol, inositol monophosphate and calcium levels, as well as on early neuronal injury, were studied in old (18 months) male rats. In old rats, a dose of 8.7 mg/kg of MO caused convulsions similar to those reported earlier in parallel experiments with young male (10 weeks) rats using a dose of 39.2 mg/kg [1,2]. In the convulsing old male rats, MO caused a transient decrease of cerebral inositol 1 h post MO in the piriform cortex and thalamus, whereas more persistent decreases of inositol occurred in the frontal cortex and the cerebellum. In the non-convulsing rats, a decrease of inositol was only seen in the cerebellum. Cerebral inositol-1-phosphate (Ins 1P) increased in all brain regions of convulsing rats, whereas Ins 1P did not change in the non-convulsing rats. Brain Ca 2+ increased post MO in convulsing and non-convulsing rats in the frontal cortex, caudate and thalamus; in the piriform cortex and hippocampus increases of Ca 2+ were only seen in the convulsing rats. Inositol-4-phosphate (Ins4P) remained stable in all MO-exposed rats. MO-induced early neuronal injury occurred only in the convulsing rats and was most severe in the cortex, hippocampus and the subcortical structures. Qualitatively the effects of MO in the old and young rats were, however, similar and, therefore, probably due to cholinergic brain stimulation and subsequent increase in inositol lipid signalling. These results suggest that old rats are likely to be more sensitive than the young rats to the neurotoxic effects of MO.

Cerebral lithium, inositol and inositol monophosphates.

Cerebral regional inositol, inositol-1-phosphate (Ins1P), and inositol-4-phosphate (Ins4P), intermediates in phosphoinositide (PI) cycle, and brain lithium levels were studied in male Han:Wistar rats 24 hr after an intraperitoneal injection of a single dose (2.5-18 mEq./kg) of LiCl. A dose of LiCl higher than 5 mEq/kg caused a remarkable accumulation of Li+ in the brain. Basal brain regional inositol levels (17-22 mmol/kg) were reduced by 6-8 mmol/kg dry brain tissue at doses exceeding 5 mEq/kg of LiCl in all brain regions except the piriform cortex. However, higher doses of LiCl did not cause any further decrease in brain inositol. LiCl increased basal brain regional Ins1P levels (170-240 mumol/kg) by 0.8 mmol/kg dry brain tissue at most, and there were no consistent additional increases of Ins1P at LiCl doses exceeding 5 mEq./kg. Moreover, lithium slightly decreased regional cerebral concentrations of Ins4P. Thus, lithium-induced accumulation of Ins1P or changes of Ins4P levels do not explain lithium-induced decrease in cerebral inositol. Effects of lithium on brain P1 turnover are likely to be multifocal and to differ markedly at different concentrations of Li+ in the brain.

Potentiation of malaoxon-induced convulsions by lithium: Early neuronal injury, phosphoinositide signaling, and calcium

Convulsions, neuronal morphology, brain phosphoinositide (PI) signaling, and calcium levels were studied in rats 1, 4, and 72 hr after malaoxon (MO; 26.2 or 39.2 mg/kg ip) subsequent to pretreatment with saline or LiCl (10 meq/kg ip). The high dose of MO induced convulsions in 60% of the rats whereas the low dose was ineffective. In nonconvulsing rats, MO transiently increased cerebral inositol 1-phosphate (Ins1P), an intermediate in PI cycle, but consistently elevated brain Ins1P in convulsing rats. LiCl did not induce convulsions, but elevated the resting level of Ins1P and decreased that of inositol. Lithium also increased the potential of MO to cause convulsions but attenuated MO-induced elevations of Ins1P. Moreover, total Ca 2+ in cortex increased in LiCl-pretreated convulsing and nonconvulsing rats after MO. Astrocytic edema and cytoplasmic vacuolation and/or shrinkage of neurons in cortical layers 2–3 and in the hippocampus as well as in some subcortical structures occurred only in convulsing rats. These results suggest that PI signaling may be involved in convulsions and contribute to the early neuronal injury. Cerebral Ca 2+ elevations seemed to precede permanent neuronal injury. A target other than the inhibition of the hydrolysis of inositol phosphates may be the site of lithium's action in cholinergic convulsions.

Subacute and Chronic In Vivo Lithium Treatment Inhibits Agonist‐ and Sodium Fluoride‐Stimulated Inositol Phosphate Production in Rat Cortex

We have investigated the effects of in vivo lithium treatment on cerebral inositol phospholipid metabolism. Twice-daily treatment of rats with LiCl (3 mEq/kg) for 3 or 16 days resulted in a 25-40% reduction in agonist-stimulated inositol phosphate production, compared with NaCl-treated controls, in cortical slices prelabelled with [3H]inositol. A small effect was also seen with 5-hydroxytryptamine (5-HT) 24 h after a single dose of LiCl (10 mEq/kg). Dose-response curves to carbachol and 5-HT showed that lithium treatment reduced the maximal agonist response without altering the EC50 value. This inhibition was not affected by the concentration of LiCl in the assay buffer. Stimulation of inositol phosphate formation by 10 mM NaF in membranes prepared from cortex of 3-day lithium-treated rats was also inhibited, by 35% compared with NaCl-treated controls. Lithium treatment did not alter the kinetic profile of inositol polyphosphate formation in cortical slices stimulated with carbachol. Muscarinic cholinergic and 5-HT2 bindings were unaltered by lithium, as was cortical phospholipase C activity and isoproterenol-stimulated cyclic AMP formation. [3H]Inositol labelling of phosphatidylinositol 4,5-bisphosphate was significantly enhanced by 3-day lithium treatment. The results, therefore, indicate that subacute or chronic in vivo lithium treatment reduces agonist-stimulated inositol phospholipid metabolism in cerebral cortex; this persistent inhibition appears to be at the level of G-protein-phospholipase C coupling.

Lithium inhibits muscarinic-receptor-stimulated inositol tetrakisphosphate accumulation in rat cerebral cortex.

The effects of Li+ on carbachol-stimulated phosphoinositide metabolism were examined in rat cerebral-cortex slices labelled with myo-[2-3H]inositol. The muscarinic agonist carbachol evoked an enhanced steady-state accumulation of [3H]inositol monophosphate ([3H]InsP1), [3H]inositol bisphosphate ([3H]InsP2), [3H]inositol 1,3,4-trisphosphate ([3H]Ins(1,3,4)P3), [3H]inositol 1,4,5-trisphosphate ([3H]Ins(1,4,5)P3) and [3H]inositol tetrakisphosphate ([3H]InsP4). Li+ (5 mM), after a 10 min lag, severely attenuated carbachol-stimulated [3H]InsP4 accumulation while simultaneously potentiating accumulation of both [3H]InsP1 and [3H]InsP2 and, at least initially, of [3H]Ins(1,3,4)P3. These data are consistent with inhibition of inositol mono-, bis- and 1,3,4-tris-phosphate phosphatases to different degrees by Li+ in brain, but are not considered to be completely accounted for in this way. Potential direct and indirect mechanisms of the inhibitory action of Li+ on [3H]InsP4 accumulation are considered. The present results stress the complex action of Li+ on cerebral inositol metabolism and indicate that more complex mechanisms than are yet evident may regulate this process.