Cortical spreading depression during streptozotocin-induced hyperglycaemia in nutritionally normal and early-malnourished rats

Exploring the translational impact of type 1 diabetes on cerebral neurovascular function through ECoG-LSCI

Type 1 diabetes mellitus (T1DM) can result in complications such as retinopathy, nephropathy, and peripheral neuropathy, which can lead to brain dysfunction. In this study, we investigated the effects of T1DM on cerebral neurovascular function in mice. Streptozotocin (STZ) is known to induce T1DM in animals; thus, we used an STZ-induced diabetes model to evaluate the effects of hyperglycemia on brain morphology and neurovascular tissue. Neurovascular coupling is the connection between neuronal activity and cerebral blood flow that maintains brain function. The ECoG-LSCI technique combines electrocorticography (ECoG) and laser speckle contrast imaging (LSCI) to detect cortical spreading depression (CSD) as a marker of neurovascular coupling and measure corresponding neurovascular function. Our results suggested that in the STZ group, hyperglycemia affected excitatory neurotransmission and metabolism, leading to reductions in intercellular signaling, somatosensory evoked potential (SSEP) amplitudes, and CSD transmission rates. Western blot data further revealed that brain-derived neurotrophic factor (BDNF) and neuronal nuclear antigen levels were reduced in the STZ group. Abnormalities in glucose metabolism in the brain and increased phosphorylation of AKT and GSK3 are hypothesized to be responsible for these decreases. Overall, this study highlights the importance of glucose metabolism in normal brain physiology and demonstrates that hyperglycemia disrupts neurovascular coupling and affects cerebral neurovascular function and that the degree of CSD is positively correlated with the extent of brain tissue damage. Further research is essential to gain a complete understanding of the related mechanisms and the implications of these findings.

The Role of Metabolism in Migraine Pathophysiology and Susceptibility

Migraine is a highly prevalent and disabling primary headache disorder, however its pathophysiology remains unclear, hindering successful treatment. A number of key secondary headache disorders have headaches that mimic migraine. Evidence has suggested a role of mitochondrial dysfunction and an imbalance between energetic supply and demand that may contribute towards migraine susceptibility. Targeting these deficits with nutraceutical supplementation may provide an additional adjunctive therapy. Neuroimaging techniques have demonstrated a metabolic phenotype in migraine similar to mitochondrial cytopathies, featuring reduced free energy availability and increased metabolic rate. This is reciprocated in vivo when modelling a fundamental mechanism of migraine aura, cortical spreading depression. Trials assessing nutraceuticals successful in the treatment of mitochondrial cytopathies including magnesium, coenzyme q10 and riboflavin have also been conducted in migraine. Although promising results have emerged from nutraceutical trials in patients with levels of minerals or vitamins below a critical threshold, they are confounded by lacking control groups or cohorts that are not large enough to be representative. Energetic imbalance in migraine may be relevant in driving the tissue towards maximum metabolic capacity, leaving the brain lacking in free energy. Personalised medicine considering an individual's deficiencies may provide an approach to ameliorate migraine.

Plasma Glucose Levels Increase During Spontaneous Attacks of Migraine With and Without Aura

OBJECTIVE

To investigate plasma glucose changes during the ictal state of migraine compared to the interictal state.

BACKGROUND

Previous studies suggest abnormal glucose metabolism in migraine patients during and outside of attacks. It is not known if plasma glucose levels change during spontaneous migraine attacks.

METHODS

Plasma glucose levels were measured during and outside of spontaneous migraine attacks with and without aura. Plasma glucose values were corrected for diurnal variation of plasma glucose by subtracting the difference between the moving average (intervals of 2 hours) and overall mean from the plasma glucose values.

RESULTS

This was a sub-study of a larger study conducted at Rigshospitalet Glostrup in the Capital Region of Denmark. Thirty-one patients (24 F, 7 M, 13 with aura, 18 without aura) were included in the study. Mean time from attack onset to blood sampling was 7.6 hours. Mean pain at the time of investigation was 6 on a 0-10 verbal rating scale. Plasma glucose was higher ictally compared to the interictal phase (interictal mean: 88.63 mg/dL, SD 11.70 mg/dL; ictal mean: 98.83 mg/dL, SD 13.16 mg/dL, difference 10.20 mg/dL, 95% CI = [4.30; 16.10]), P = .0014). The ictal increase was highest in patients investigated early during attacks and decreased linearly with time from onset of migraine (-1.57 mg/dL/hour from onset of attack, P = .020). The attack-related increase in blood glucose was not affected by pain intensity or presence of aura symptoms.

CONCLUSIONS

We demonstrated higher plasma glucose values during spontaneous migraine attacks, independent of the presence of aura symptoms and not related to pain intensity, peaking in the early phase of attacks. Additional studies are necessary to confirm our findings and explore the possible underlying mechanisms.

Environmental enrichment reduces brain excitability in adult rats overnourished during lactation

OBJECTIVE

This study aimed to analyze whether exposure to environmental enrichment (EE) during the juvenile phase of life interferes with the electrical activity of the adult rat brain. In addition, the present research also investigated whether this putative effect on brain electrical activity could be affected by prior overnutrition during lactation. Electrophysiology was measured through cortical spreading depression (CSD), a phenomenon related to brain excitability.

METHODS

Wistar rats were suckled in litters of either nine or three pups, forming the nourished (N) or overnourished (ON) groups, respectively. At 36 days old, half of the animals from each nutritional condition were exposed to EE. The other half was kept in the standard environment (SE). At 90-120 days of life, each animal was anesthetized for CSD recordings.

RESULTS

Overnutrition during lactation caused increases (p < 0.05) in body and brain weights. The EE decelerated CSD propagation velocity regardless of nutritional state during lactation (p < 0.001). The CSD deceleration in the N-EE group was 23.8% and in the ON-EE group was 15% in comparison with the N-SE and ON-SE groups, respectively.

CONCLUSION

Our data demonstrated that EE exposure in the juvenile phase of the rat's life reduced brain excitability, and this effect was observed even if animals were overnourished during lactation. An EE could be considered an adjuvant therapeutic resource to modulate brain excitability.

Manipulation of rat litter size during suckling influences cortical spreading depression after weaning and at adulthood

Nutritional conditions early in life constitute one environmental factor that can influence brain electrophysiological features. Cortical spreading depression (SD) is a brain electrophysiological phenomenon that can be altered by the early nutritional status of organism. SD-velocity changes were presently studied in young (30-40 days old) and adult (90-120 days) rats suckled in litters formed by 3, 6, or 12 pups (called respectively small (S), medium (M) and large (L) litters). Body weights and SD propagation velocities in the 3 groups varied, respectively in an inverse and direct way, in relation to the litter sizes. The present investigation provides the first systematic description of the effectiveness of favorable and unfavorable lactation conditions (respectively suckling in S and L litters) in altering cortical SD-propagation. The results confirm previous evidence in favor of permanent or at least long-lasting SD-changes associated to the prevailing nutritional status during the period of fast brain development.

Malnutrition and REM-sleep Deprivation Modulate in Rats the Impairment of Spreading Depression by a Single Sub-convulsing Dose of Pilocarpine

This study aimed to investigate the effect of a single injection of pilocarpine upon the phenomenon of cortical spreading depression (SD), in adult rats submitted to early malnutrition and/or to REM-sleep deprivation for 72h prior to the SD-recordings. The SD was recorded continuously for 3-4h in 13 well-nourished (W) and 15 early-malnourished (M) adult rats. One to two hours after the beginning of the recording session, a sub-convulsing intraperitoneal (i.p.) injection of pilocarpine (190mg/kg) was applied and its effects on SD were studied during the rest of the recording session. Pilocarpine reduced markedly the ECoG amplitudes in all animals and decreased the SD velocity of propagation in the M-, but not in the W-rats, as compared with the pre-drug values for the same animals. In additional 9W- and 10 M-animals, REM-sleep deprivation was induced during the 72 h preceding the SD-recording session. This condition enhanced the pilocarpine effects on SD in the W-, but not in the M-rats, as compared to the respective non-deprived (ND) groups. The results indicate an important acute cholinergic influence on SD, acting by means of pilocarpine-activated muscarinic receptors. This effect seems to be differentially modulated by sleep deprivation and malnutrition.

Exercise and food ad libitum reduce the impact of early in life nutritional inbalances on nitrergic activity of hippocampus and striatum

Nutritional imbalances were produced by varying litter size pups per dam: 3 (small), 6 (medium), and 12 (large). On the 21st day, 4 subjects of each litter, were sacrificed and the remaining were grouped, 2 per cage, with or without running wheels, with food and water ad libitum. Adult subjects were tested in water maze, their brains processed for NADPH-diaphorase histochemistry and quantified by densitometry. No differences were detected in water maze. At 21st day, S and L compared with M presented reduced NADPH-d in the stratum molecular of dentate gyrus (DG), stratum lacunosum of CA1 and in all CA3 layers but not in the striatum. On the 58th day, actvity remained low in S and L in CA3 and striatum and L in CA1 and DG. Voluntary exercise increased NADPH-d in DG, CA1, CA3, and striatum in S, and in the stratum lacunosum of CA1 and CA3 in L.

Fluoxetine inhibits cortical spreading depression in weaned and adult rats suckled under favorable and unfavorable lactation conditions

Wistar rats (n = 58) were injected subcutaneously during the lactation period with fluoxetine (5, 10, 20 or 40 mg/kg/day) and cortical spreading depression (SD) was recorded immediately after weaning (25-30 days of life). An additional group (10 mg/kg; n = 8) was SD-recorded at 60-70 days. As compared to the saline-injected (n = 24) or "ingenuous" (n = 16) controls, fluoxetine dose-dependently reduced (P < 0.05) SD-velocities in the young rats by 4, 6, 16 and 15%, respectively, and in adult rats by 13%. In another experiment (26 adult rats), topical cortical application of fluoxetine (5 and 10 mg/ml solutions over the intact dura-mater for 10 min; n = 12 and 14, respectively) dose-dependently reduced SD-velocity (7.6% and 43.3% maximal reductions; P < 0.05). SD-propagation was blocked in 4 out of the 14 W-rats topically treated with the highest fluoxetine concentration (10 mg/ml). This topical fluoxetine effect was reverted after flushing the treated region with saline. In additional, 58 early-malnourished rats, fluoxetine applied during the suckling period (10 mg/kg/day, s.c.) and topically (10 mg/ml) also reduced (P < 0.05) SD-velocities by 18 and 22% for the systemic treatment (young and adult animals, respectively) and by 22.4% for the topical one. The present fluoxetine action supports the hypothesis of an antagonistic serotoninergic influence on SD, as previously suggested in experiments using other serotoninergic drugs. Data also suggest that early malnutrition does not greatly affect fluoxetine effects on SD.

Characterization of cortical spreading depression in adult well-nourished and malnourished rats submitted to the association of pilocarpine-induced epilepsy plus streptozotocin-induced hyperglycemia

Spreading depression was characterized in adult rats rendered epileptic by pilocarpine (350 mg/kg, i.p.) and thereafter made hyperglycemic with (i.p.) 60 mg/kg streptozotocin. Groups treated with only one of the above drugs, as well as control groups treated with their vehicles (saline and citrate buffer, respectively) were also studied. The animals treated with pilocarpine or streptozotocin presented, as a common feature, a reduction in the spreading depression propagation rate. However, they differed by the fact that pilocarpine, in some cases, blocked spreading depression propagation, whereas streptozotocin did not block it at all. In early-malnourished animals, streptozotocin-effects, but not pilocarpine-effects on spreading depression were attenuated. The treatment with both drugs did not potentiate their individual reducing effects on spreading depression propagation, irrespective of the animals' early nutritional status. These results extend previous observations on rats treated with both drugs separately, confirming their impairing action on spreading depression propagation. They also indicate that early malnutrition is more effective in changing the streptozotocin effects on spreading depression, as compared to the pilocarpine-effects. Since such effects were observed at adulthood, they indicate that the early malnutrition-induced cortical changes responsible for the here-described effects are long-lasting.

l-arginine treatment early in life influences NADPH-diaphorase neurons in visual cortex of normal and early-malnourished adult rats

This study investigated the effects of repeated l-arginine administration during lactation, combined with different suckling conditions, on morphometric parameters of primary visual cortex NADPH-diaphorase-positive neurons. Wistar rat pups reared in "normal-size litters" or "large litters" (N- and L-conditions; litters formed by 6 and 12 pups, respectively) received, from postnatal day 7 to 28, either arginine (300 mg/kg/day, per gavage) or distilled water (control). At 90-120 days of life, they were perfused with saline + formaldehyde, and their brains were processed for histochemical reaction to reveal NADPH-diaphorase-positive neurons (malic enzyme indirect method). Compared to the normal-size litters, L-rats had lower body weights (P < 0.05), confirming the effectiveness of the L-condition in affecting pup development. Concerning NADPH-d histochemistry, arginine treatment was associated with increased (P < 0.05) density of dendrite varicosities and of dendrite branching frequency, suggesting a plastic response of the developing brain to that treatment, even in previously malnourished rats. No difference was seen, however, in dendrite orientation, total number of neurons, soma area and perimeter, as well as dendrite bifurcation points, fractal dimension, and area and volume of dendrite field, suggesting that NADPH-d cells are resistant to arginine and nutritional changes, regarding these features. Data are considered of interest for studies of synaptic plasticity during neural development and its relationships to aggressive agents like malnutrition.

After-effects of transcranial direct current stimulation (tDCS) on cortical spreading depression

Abnormal cortical excitability influences susceptibility to cortical spreading depression (CSD) in migraine. Because transcranial direct current stimulation (tDCS) is capable of inducing lasting changes of cortical excitability, we investigated the after-effects of tDCS on the propagation velocity of CSD in the rat. Twenty-five anesthetised rats received either anodal, cathodal or sham tDCS. The stimulation was applied for 20 min at a current strength of 200 microA after the recording of three baseline CSD measurements. Starting 5 min after tDCS, a further three CSDs were elicited and CSD velocity recorded at intervals of 20 min. tDCS and CSD recording was performed under anaesthesia with chloralose and urethane. As compared to the baseline velocity of 3.14 mm/min, anodal tDCS induced a significant increase of propagation velocity during the first post-tDCS recording (3.49 mm/min). In contrast to anodal tDCS, neither cathodal tDCS nor sham tDCS, which consisted of an initial ramped DC stimulation lasting only 20 s, showed a significant effect on CSD propagation velocity. As anodal tDCS is known to induce a lasting increase of cortical excitability in the clinical setting, our results support the notion that CSD propagation velocity reflects cortical excitability. Since cortical excitability and susceptibility to CSD is elevated in migraine patients, anodal tDCS - by increasing cortical excitability - might increase the probability of migraine attack in these patients, even beyond the end of its application.

Lasting accelerative effects of 1 Hz and 20 Hz electrical stimulation on cortical spreading depression: relevance for clinical applications of brain stimulation

Clinical applications of brain stimulation have been increasing during the last decade; however, the mechanisms of action remain unknown. One proposed mechanism of action is that repetitive stimulation modulates cortical excitability. Herein, we explore the question of whether repetitive electric stimulation increases cortical excitability as indexed by the cortical spreading depression. Twenty-four Wistar rats were divided into three groups according to the treatment: sham, 1-Hz and 20-Hz stimulation. Stimulation was applied to the left frontal cortex through a pair of epidurally implanted silver-wire electrodes. The cortical spreading depression-features were analysed at three time points (one day before, one day after and 2 weeks after treatment) in both the stimulated and unstimulated hemisphere. A 3 x 2 x 3 factorial anova with repeated measures showed significant differences in the main effect of time (P < 0.0001), hemisphere (P = 0.0002) and stimulation group (P = 0.008). The interaction between time vs. hemisphere vs. stimulation group was also significant (P < 0.0001). Posthoc analysis demonstrated that 1-Hz and 20-Hz repetitive electrical stimulation significantly increased the velocity of cortical spreading depression in the stimulated hemisphere. Furthermore, 20-Hz stimulation showed a greater effect on cortical spreading depression compared to 1-Hz stimulation. The results show that 1-Hz and 20-Hz repetitive electrical stimulation results in an increase in cortical spreading depression velocity that is associated with the frequency and the hemisphere of stimulation. Furthermore, the effects are found to be long lasting. We believe that these findings have strong relevance to support the clinical application of therapies involving electrical stimulation for diseases of reduced cortical excitability.

Citalopram has an antagonistic action on cortical spreading depression in well-nourished and early-malnourished adult rats

Adult, well-nourished (W) and early-malnourished (M) male Wistar rats were injected intraperitoneally for 7 days with 20 mg/kg CIT and cortical spreading depression (CSD) was recorded for 4 h on the day following the treatment. M-animals presented lower body weights, as well as higher CSD velocities of propagation, than the W ones, as previously reported. Compared to saline-injected controls, rats treated with CIT for 7 days presented comparable body weights and lower mean CSD velocities, per hour of recording, the differences being significant at the second hour (3.29+/-0.31 versus 3.56+/-0.40 mm/min; P < 0.05). Topical, cortical application of CIT (1- and 5 mg/ml solutions over the intact dura-mater) reduced dose-dependently the CSD velocity (maximal reductions of 16.3 and 55.8% for the 1 and 5 mg/ml solutions, respectively; P < 0.05), as well as the amplitude of the CSD-slow potential change (58.2 and 88.3%). In three out of seven W-rats and in one out of seven M-rats, topical CIT (5 mg/ml) blocked CSD propagation. The effects were reverted by flushing the treated region with saline. In the M-groups, CIT affected CSD in the same manner as in the W ones. The results reinforce previous evidence for an antagonistic influence of the serotoninergic activity on CSD.