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

Updated review on the link between cortical spreading depression and headache disorders

INTRODUCTION

Experimental animal studies have revealed mechanisms that link cortical spreading depression (CSD) to the trigeminal activation mediating lateralized headache. However, conventional CSD as seen in lissencephalic brain is insufficient to explain some clinical features of aura and migraine headache.

AREAS COVERED

The importance of CSD in headache development including dysfunction of the thalamocortical network, neuroinflammation, calcitonin gene-related peptide, transgenic models, and the role of CSD in migraine triggers, treatment options, neuromodulation and future directions are reviewed.

EXPERT OPINION

The conventional understanding of CSD marching across the hemisphere is invalid in gyrencephalic brains. Thalamocortical dysfunction and interruption of functional cortical network systems by CSD, may provide alternative explanations for clinical manifestations of migraine phases including aura. Not all drugs showing CSD blocking properties in lissencephalic brains, have efficacy in migraine headache and monoclonal antibodies against CGRP ligand/receptors which are effective in migraine treatment, have no impact on aura in humans or CSD properties in rodents. Functional networks and molecular mechanisms mediating and amplifying the effects of limited CSD in migraine brain remain to be investigated to define new targets.

Undernutrition - thirty years of the Regional Basic Diet: the legacy of Naíde Teodósio in different fields of knowledge

Undernutrition is characterized by an imbalance of essential nutrients with an insufficient nutritional intake, a disorder in which the clinical manifestations in most cases are the result of the economic and social context in which the individual lives. In 1990, the study by the medical and humanitarian Naíde Teodósio (1915-2005) and coworkers, which formulated the Regional Basic Diet (RBD) model for inducing undernutrition, was published. This diet model took its origin from the observation of the dietary habits of families that inhabited impoverished areas from the Pernambuco State. RBD mimics an undernutrition framework that extends not only to the Brazilian population, but to populations in different regions worldwide. The studies based on RBD-induced deficiencies provide a better understanding of the impact of undernutrition on the pathophysiological mechanisms underlying the most diverse prevalent diseases. Indexed papers that are analyzed in this review focus on the importance of using RBD in different areas of knowledge. These papers reflect a new paradigm in translational medicine: they show how the study of pathology using the RBD model in animals over the past 30 years has and still can help scientists today, shedding light on the mechanisms of prevalent diseases that affect impoverished populations.

Systematic review of the pharmacological agents that have been tested against spreading depolarizations

Spreading depolarization (SD) occurs alongside brain injuries and it can lead to neuronal damage. Therefore, pharmacological modulation of SD can constitute a therapeutic approach to reduce its detrimental effects and to improve the clinical outcome of patients. The major objective of this article was to produce a systematic review of all the drugs that have been tested against SD. Of the substances that have been examined, most have been shown to modulate certain SD characteristics. Only a few have succeeded in significantly inhibiting SD. We present a variety of strategies that have been proposed to overcome the notorious harmfulness and pharmacoresistance of SD. Information on clinically used anesthetic, sedative, hypnotic agents, anti-migraine drugs, anticonvulsants and various other substances have been compiled and reviewed with respect to the efficacy against SD, in order to answer the question of whether a drug at safe doses could be of therapeutic use against SD in humans.

Spreading depression features and Iba1 immunoreactivity in the cerebral cortex of developing rats submitted to treadmill exercise after treatment with monosodium glutamate

Physical exercise and excessive consumption of monosodium glutamate (MSG) can affect the morphological and electrophysiological organization of the brain during development. However, the interaction of both factors remains unclear. We analyzed the effect of this interaction on the excitability-related phenomenon known as cortical spreading depression (CSD) and the microglial reaction expressed as Iba1-immunolabeled cells in the rat motor cortex. MSG (2g/kg or 4g/kg) was administered every other day during the first 14 postnatal days. Treadmill exercise started at 21-23 days of life and lasted 3 weeks, 5 days/week, for 30min/day. At 45-60 days, CSD was recorded for 4h at two cortical points and the CSD parameters (velocity, amplitude, and duration of the negative potential change) calculated. Confirming previous observations, exercised rats presented with lower CSD velocities (3.29±0.18mm/min) than the sedentary group (3.80±0.18mm/min; P<0.05). MSG increased CSD velocities in the exercised rats compared to saline-treated and exercised animals in a dose-dependent manner (3.49±0.19, 4.05±0.18, and 3.27±0.26 for 2g/kg MSG, 4g/kg MSG, and saline, respectively; P<0.05). The amplitude (ranging from 14.3±5.9 to 18.7±6.2mV) and duration (46.7±11.1 to 60.5±11.6s) of the negative slow potential shift of the CSD were similar in all groups. Both exercise and MSG treatment increased Iba1 immunolabeling. The results confirm that physical exercise decelerates CSD propagation. However, it does not impede the CSD-accelerating action of MSG. These effects were accompanied by a cortical microglia reaction. Therefore, the data suggest that treadmill exercise early in life can influence the development of cortical electrical activity.

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.

Pharmacological targeting of spreading depression in migraine

Migraine, particularly with aura, is a genetically heterogeneous disorder of ion channels, pumps or transporters associated with increased cortical excitability. Spreading depression, as one reflection of hyperexcitability, is the electrophysiological event underlying aura symptoms and a trigger for headache. Endogenous (e.g., genes and hormones) and exogenous factors (e.g., drugs) modulating migraine susceptibility have also been shown to modulate spreading depression susceptibility concordantly, suggesting that spreading depression can be a relevant therapeutic target in migraine. In support of this, several migraine prophylactic drugs used in clinical practice have been shown to suppress spreading depression susceptibility as a probable mechanism of action, despite belonging to widely different pharmacological classes. Hence, susceptibility to spreading depression can be a useful preclinical model with good positive and negative predictive value for drug screening.

Differential effects of physical exercise and L-arginine on cortical spreading depression in developing rats

OBJECTIVE

We investigated the effect of early-in-life administration of L-arginine, combined with physical exercise, on cortical spreading depression (CSD) in young and adult rats.

METHODS

L-arginine (300 mg/kg/day, n = 40) or distilled water (vehicle, n = 40) was given to the rats during postnatal days 7-35 by gavage. Physical exercise (treadmill) was carried out during postnatal days 15-35 in half of the animals in each gavage condition described above. The other half (non-exercised) was used for comparison. When the animals reached 35-45 days (young groups) or 90-120 days of age (adult) CSD was recorded on two cortical points during 4 hours and CSD propagation velocity was calculated.

RESULTS

L-arginine-treated + exercised rats had increased body weight, but not brain weight, in adult age compared to L-arginine + non-exercised ones (P < 0.05). In both young and adult animals, L-arginine increased, whereas exercise decreased the CSD propagation velocity. Analysis of variance revealed a significant interaction between gavage treatment and age (P < 0.001), and also between gavage treatment and exercise (P = 0.004), but not between age and exercise. An additional control group of young rats, treated with 300 mg/kg of L-histidine, presented CSD velocities comparable to the corresponding water-treated controls, suggesting that the CSD acceleration seen in the L-arginine group was an L-arginine-specific effect, rather than an effect due to a non-specific amino acid imbalance.

DISCUSSION

L-arginine and exercise affect CSD differentially (L-arginine accelerated, while exercise decelerated CSD), and both effects did interact. Probably, they depend on developmental plasticity changes associated with the treatments.

Headache endocrinological aspects

In this chapter we review the current understanding of how hormones, neurohormones, and neurotransmitters participate in the pain modulation of primary headaches. Stressful conditions and hormones intimately implicated in headache neurobiology are also discussed. With the recent progress in neuroimaging techniques and the development of animal models to study headache mechanisms, the physiopathology of several of the primary headaches is starting to be better understood. Various clinical characteristics of the primary headaches, such as pain, autonomic disturbances, and behavioral changes, are linked to hypothalamic brainstem activation and hormonal influence. Headache is greatly influenced by the circadian circle. Over the millennia the nervous system has evolved to meet changing environmental conditions, including the light-dark cycle, in order to ensure survival and reproduction. The main elements for synchronization between internal biological events and the external environment are the pineal gland and its main secretory product, melatonin. Melatonin is believed to be a significant element in migraine and in other headache disorders, which has implications for treatment. A potential therapeutic use of melatonin has been considered in several headache syndromes. In short, primary headaches are strongly influenced by physiological hormonal fluctuations, when nociceptive and non-nociceptive pathways are differentially activated to modulate the perception of pain.

Spreading depression: from serendipity to targeted therapy in migraine prophylaxis

Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

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.

Shrimp carotenoids protect the developing rat cerebral cortex against the effects of ethanol on cortical spreading depression

Cortical spreading depression is a neural phenomenon present in several animal species. Spreading depression features, like velocity of propagation, depends on several chemical and metabolic factors, as for example, anti-oxidants. Here we studied spreading depression-velocity changes in weaned rat-pups born from dams treated on a daily basis, either during gestation or lactation, with a carotenoid ethanolic extract (30 microg/kg/day) prepared from shrimp waste (heads). These pups were compared with age-mated ones, whose mothers were treated either with the vehicle (ethanol) or with distilled water. Compared to the distilled water-group (mean values, in mm/min, per hour of recording ranging from 3.02+/-0.26 to 3.15+/-0.27 [treatment during gestation; n=7], and from 3.03+/-0.25 to 3.22+/-0.30 [lactation; n=11]), ethanol-treated rats displayed higher spreading depression-velocities (from 3.74+/-0.06 to 3.82+/-0.08 [gestation; n=7], and from 4.26+/-0.32 to 4.33+/-0.34 [lactation; n=11]; p<0.05). Compared to the ethanol-group, carotenoid-treatment lead to lower spreading depression-velocities (p<0.05), ranging from 3.38+/-0.09 to 3.42+/-0.12, n=7 (gestation) and 3.58+/-0.13 to 3.62+/-0.17, n=12 (lactation). Carotenoid-treatment during lactation was shown to be significantly more effective than that during gestation (p<0.05), in lowering spreading depression-velocity. The results suggest a protective action of shrimp carotenoids against the ethanol effects on spreading depression. This protective effect could be related to the carotenoid antioxidant properties, as previously indicated by evidence showing spreading depression-effects of other antioxidants.

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.

Spreading depression in vivo potentiates electrically-driven responses in frog optic tectum

This is the first description of an in vivo potentiation phenomenon associated to spreading depression (SD) in the frog optic tectum. Field potential responses electrically-elicited from the optic tract and recorded in the optic tectum disappeared during KCl-elicited SD and recovered 10-20 min thereafter. Post-SD responses reached amplitudes 10-30% higher than their pre-SD values (P<0.05), indicating a potentiation effect. Current source density analysis of the tectal depth profiles of field-potential responses, as well as the calculation of the post-SD intratectal conductance changes, also supported the potentiation phenomenon. This in vivo potentiation lasted for 40-90 min, suggesting a post-SD enhancement of synaptic transmission, which may be important in understanding mechanisms of brain disfunctions like epilepsy.