Javier Franco-Pérez

Radiation-Induced Neuroinflammation and Radiation Somnolence Syndrome

Cranial irradiation remains a standard treatment for malignant and benign brain diseases. Although this procedure helps to lengthen the life expectancy of the patient, the appearance of adverse effects related to radiation-induced injury is inevitable. Radiation somnolence syndrome (RSS) has been described as a delayed effect observed mainly after whole-brain radiotherapy in children. The RSS was first linked to demyelination, but more recently it has been proposed that the inflammatory response plays a primary role in the aforementioned syndrome. To evaluate the feasibility of this hypothesis, we explored previous work about RSS and reviewed published research that included measurements of the inflammatory response in models of brain exposure to ionizing radiation. Pro-inflammatory cytokines such as interleukin-1β, tumor necrosis factor-α, interleukin-6 and interleukin-18 as well as other inflammatory markers such as cyclooxygenase-2, prostaglandin E₂, glial fibrillary acid protein, intercellular adhesion molecule-1 and nuclear factor-κB appear to be involved in the brains response to radiation. However, certain publications have described the somnogenic effects of these cytokines and inflammatory markers. Although the radiation response is a complex phenomenon that involves several molecular and cellular processes, we propose that inflammation may be closely related to the adverse effects of brain irradiation and therefore to the etiology of RSS.

The effects of ozone exposure and associated injury mechanisms on the central nervous system

Abstract Ozone (O3) is a component of photochemical smog, which is a major air pollutant and demonstrates properties that are harmful to health because of the toxic properties that are inherent to its powerful oxidizing capabilities. Environmental O3 exposure is associated with many symptoms related to respiratory disorders, which include loss of lung function, exacerbation of asthma, airway damage, and lung inflammation. The effects of O3 are not restricted to the respiratory system or function – adverse effects within the central nervous system (CNS) such as decreased cognitive response, decrease in motor activity, headaches, disturbances in the sleep-wake cycle, neuronal dysfunctions, cell degeneration, and neurochemical alterations have also been described; furthermore, it has also been proposed that O3 could have epigenetic effects. O3 exposure induces the reactive chemical species in the lungs, but the short half-life of these chemical species has led some authors to attribute the injurious mechanisms observed within the lungs to inflammatory processes. However, the damage to the CNS induced by O3 exposure is not well understood. In this review, the basic mechanisms of inflammation and activation of the immune system by O3 exposure are described and the potential mechanisms of damage, which include neuroinflammation and oxidative stress, and the signs and symptoms of disturbances within the CNS caused by environmental O3 exposure are discussed.

Quinine, a selective gap junction blocker, decreases REM sleep in rats.

Electrical synapses are formed by gap junctions that allow the direct communication between neurons, the intercellular transference of ions and small molecules as well as the electrical coupling of the cells. Electrical coupling in neurons is mediated by the gap junction protein connexin36. There are reports about the presence of electrical coupling in the sublaterodorsal nucleus and pedunculopontine nucleus, which have been implicated in the modulation of the rapid eye movement sleep. In the present study, rats were used to examine the possible changes on the sleep-wake states after intracerebroventricular administration of several doses of quinine, a selective blocker of gap junctions formed by connexin36. The results showed that quinine significantly increased the time spent in wakefulness and decreased the time spent in slow wave sleep along the 24h of polygraphic recording. The three doses used of quinine caused a significant decrease of rapid eye movement sleep along the light phase; however, only one dose extended such effect until the darkness phase. The changes on sleep-wake states of the rat after the blockage of gap junctions formed by connexin36 suggest that electrical synapses could contribute to the regulation of sleep-wake states in concert with the well-known chemical neurotransmission.

Sleep deprivation and sleep recovery modifies connexin36 and connexin43 protein levels in rat brain.

Gap junctional communication is mainly mediated by connexin36 and connexin43 in neurons and astrocytes, respectively. It has been suggested that connexin36 allows electrical coupling between neurons whereas connexin43 participates in several process including release of ATP. It was recently reported that blockage of gap junctional communication mediated by connexin36 can disrupt the sleep architecture of the rat. However, there is no experimental approach about effects of sleep deprivation on connexins expression. Therefore, we examined in adult male Wistar rats whether protein levels of connexin36 and connexin43 change in pons, hypothalamus, and frontal cortex after 24 h of total sleep deprivation and 4 h of sleep recovery. Western blot revealed that total sleep deprivation significantly decreases the levels of connexin36 in the hypothalamus and this decrease maintains after sleep recovery. Meanwhile, connexin43 is not altered by total sleep deprivation but interestingly the sleep recovery period induces an increase of this connexin. These results suggest that electrical coupling between hypothalamic neurons could be altered by sleep deprivation and that sleep recovery drives changes in connexin43 expression probably as a mechanism related to ATP release and energy regulation during sleep.

Gap Junction Blockers: An Overview of their Effects on Induced Seizures in Animal Models.

Abstract: Background Gap junctions are clusters of intercellular channels allowing the bidirectional pass of ions directly into the cytoplasm of adjacent cells. Electrical coupling mediated by gap junctions plays a role in the generation of highly synchronized electrical activity. The hypersynchronous neuronal activity is a distinctive characteristic of convulsive events. Therefore, it has been postulated that enhanced gap junctional communication is an underlying mechanism involved in the generation and maintenance of seizures. There are some chemical compounds characterized as gap junction blockers because of their ability to disrupt the gap junctional intercellular communication. Objective Hence, the aim of this review is to analyze the available data concerning the effects of gap junction blockers specifically in seizure models. Results Carbenoxolone, quinine, mefloquine, quinidine, anandamide, oleamide, heptanol, octanol, meclofenamic acid, niflumic acid, flufenamic acid, glycyrrhetinic acid and retinoic acid have all been evaluated on animal seizure models. In vitro, these compounds share anticonvulsant effects typically characterized by the reduction of both amplitude and frequency of the epileptiform activity induced in brain slices. In vivo, gap junction blockers modify the behavioral parameters related to seizures induced by 4-aminopyridine, pentylenetetrazole, pilocarpine, penicillin and maximal electroshock. Conclusion Although more studies are still required, these molecules could be a promising avenue in the search for new pharmaceutical alternatives for the treatment of epilepsy.

Effect of Acetaldehyde on Behavioral and Neurochemical Changes Induced by MK-801 in Rats

Alterations in motor activity related to dopamine changes in some brain regions have been described as consequences of the modifications produced by systemic administration of MK‐801 (a noncompetitive NMDA receptor antagonist) in rats. Acetaldehyde (ACH), the main metabolite of ethanol, has been implicated in different alterations in the central nervous system after ethanol ingestion. ACH might exert some control on dopaminergic transmission through the formation of other compounds with dopamine, which eventually may modify dopamine content and its metabolism. In order to evaluate such a hypothesis, we used Wistar rats in the present study to evaluate the effect of ACH on locomotor alterations and dopamine metabolism changes induced by MK‐801. Our results show that the MK‐801‐treated group had a significant increase in locomotor activity. In contrast, we did not find significant differences in locomotion tests after ACH administration. However, the group to which both drugs were administered showed a significant decrease in locomotor activity compared with those given MK‐801 alone. Neurochemical analysis showed an increase in dopamine content in the striatum and frontal cortex after MK‐801 administration, however; the increase was reversed by giving 200 mg/kg of ACH. These results indicate that ACH can produce an antagonic‐like effect on locomotor alterations and dopamine content changes induced by MK‐801, thus modulating the MK‐801‐induced hyperlocomotion by interfering with dopamine metabolism.

Unilateral microinjection of carbenoxolone into the pontis caudalis nucleus inhibits the pentylenetetrazole-induced epileptiform activity in rats

Pontine reticular formation (PRF) is involved in the generation and maintenance of generalized epileptic seizures. Carbenoxolone (CBX) is a gap junction blocker with anticonvulsant properties. Therefore, the present study was designed to explore the effects of CBX microinjected into the pontis caudalis nucleus (PnC) on generalized tonic-clonic seizures (GTCS) and epileptiform activity induced by pentylenetetrazole (PTZ). All control rats presented GTCS after a single dose of PTZ. The microinjection of CBX into the PnC reduced the GTCS incidence induced by PTZ. Moreover, the CBX significantly increased the latency to the first myoclonic jerk. Additionally, CBX significantly decreased the spectral power and the amplitude of the epileptiform activity induced by PTZ. By contrast, the microinjection of a gap junction opener (trimethylamine) did not cause anticonvulsant effects and even increased the duration of the GTCS. These findings suggest that the PnC is a particular nucleus where the CBX could exert its action mechanisms and elicit anticonvulsant effects.

Whole-brain irradiation increases NREM sleep and hypothalamic expression of IL-1β in rats

Abstract Purpose: Although it has mainly been described qualitatively, whole brain irradiation induces somnolence in patients with malignant diseases. Therefore, we used a rat model to quantify the effects of irradiation of healthy brain tissue on both sleep-wake patterns and the expression of the pro-inflammatory cytokine interleukin-1β (IL-1β), which is known to induce sleep. Materials and methods: Different groups were examined at three time points after irradiation (1 day, 30 days and 60 days). Polysomnographic recordings were performed on each rat before and after total cranial irradiation (12 Gy). IL-1β protein levels in several brain regions were assessed by enzyme-linked immunosorbent assays, and site-specific immunoreactivity was observed by immunofluorescence. Results: We found that both non-rapid eye movement sleep and IL-1β protein expression in the hypothalamus increased 30 days after irradiation. Conclusions: Whole brain irradiation increases sleep in our rat model, and this finding is similar to qualitative reports from patients. Because IL-1β has been proposed as a sleep-promoting molecule, we propose that the polysomnographic results may be attributable, at least in part, to the delayed overexpression of IL-1β in the hypothalamus.

Sleep and brain monoamine changes produced by acute and chronic acetaldehyde administration in rats.

Acetaldehyde, the most toxic metabolite of ethanol, has been implicated in many toxic effects of ethanol. In the present study, we used rats to investigate the possible changes on the sleep-wake cycle and brain regional concentrations of noradrenaline and serotonin after intraperitoneal administration of several doses of acetaldehyde. Results showed that acetaldehyde significantly decreases the time spent in rapid eye movements sleep and wakefulness and increases the time spent in slow-wave sleep. The neurochemical analysis showed that acetaldehyde significantly increases the 5-hydroxyindolacetic acid content and 5-hydroxyindolacetic acid/serotonin ratio at the bulb and pons. These results suggest that acetaldehyde modifies the metabolism of serotonin which has been implicated in the onset and sustaining of the sleep episodes occurring along the sleep-wake cycle.

Quinine and carbenoxolone enhance the anticonvulsant activity of some classical antiepileptic drugs

Abstract Objective Quinine (QUIN) and carbenoxolone (CNX) elicit anticonvulsant effects typically characterized by the reduction of the epileptiform activity as well as changes in behavioral parameters related to seizures. Therefore, the aim of this study was to analyze the effects of these molecules on the anticonvulsant activity of some classical antiepileptic drugs. Methods Male Wistar rats were used. Valproate (VPA), phenytoin (PHT), or carbamazepine (CBZ) was administered at sub-therapeutic doses for intraperitoneal via. Subsequently, animals were administered with a single dose of QUIN or CNX. The anticonvulsant activity was evaluated with the maximal electroshock (MES) test and pentylenetetrazole (PTZ) administration. Additionally, the plasma levels of CBZ were determined using an HPLC method. Results All the control rats presented generalized tonic–clonic seizures after the MES test or the administration of PTZ. For the MES test, all of the antiepileptic drugs increased their anticonvulsant activity when were co-administered with QUIN. For the PTZ test, only the combination CBZ plus QUIN significantly increased the percentage of protection against the generalized tonic–clonic seizures. The co-administration of CBZ plus QUIN resulted in an augmented concentration of CBZ in plasma. Discussion The present study shows that QUIN and CNX enhance the anticonvulsant activity of some classical antiepileptic drugs. However, only the combination CBZ/QUIN had significant effects on both MES and PTZ models. Such anticonvulsant activity could be attributed to increased levels of CBZ in plasma. We propose that these molecules could improve the pharmacological actions of antiepileptic drugs administered at sub-therapeutic doses.