Karolina Kołosowska

The kynurenine pathway: a missing piece in the puzzle of valproate action?

The present study was designed to determine the role of the kynurenine pathway (KP) in the mechanism of action of valproate (VPA). Therefore, we investigated changes in the concentrations of tryptophan (TRP), kynurenic acid (KYNA), and kynurenine (KYN) in the brain and plasma following VPA administration (50, 250 and 500mg/kg i.p.). The most important findings of our study were that VPA administration produced a progressive and strong increase in the central concentrations of KYNA, KYN and TRP. Simultaneously, the TRP level in plasma declined, while the peripheral increase of KYNA in plasma was weaker and occurred earlier than in the hippocampus. Bearing in mind that the observed effect may be a result of a strong VPA-induced displacement of TRP from its binding sites to plasma albumin, we checked the effect of ibuprofen (IBU) administration (a prototypic drug used to study drug binding to serum albumin) on the KP. We found that IBU evoked a similar pattern of change in the KP activity as VPA. These new findings indicate the existence of a mechanism that could stimulate the production of KYNA in the brain after VPA administration, and may partially contribute to the mechanisms of VPA action. The results of our experiment indicate that an increase in the brains KYNA level may be achieved by TRP displacement from its binding site on plasma albumin with the administration of different drugs, including VPA, IBU, or short-chain fatty acids, with important clinical consequences.

Time course of changes in the concentrations of amino acids in the brain structures of pentylenetetrazole-kindled rats.

The results showed that the development of seizures (pentylenetetrazole, PTZ-induced kindling; PTZ was administered to rats at a subconvulsive dose of 35mg/kg three times a week, i.p.) was accompanied by a progressive recruitment of limbic structures and a characteristic pattern of changes in the brain tissue concentration of examined amino acids (ex vivo measurements, 1.5h after the last dose of PTZ). The earliest and homogenous increase in the excitatory (glutamate and alanine) and inhibitory (GABA and taurine) amino acids was observed in the entorhinal cortex (at stages 1 and 2 according to Racines scale), and this effect was maintained at the fifth stage of kindling (except for glutamate). At the fifth stage of kindling, glutamate was elevated in the amygdala, nucleus accumbens and piriform cortex, whereas alanine content was increased in the hippocampus, amygdala, striatum, nucleus accumbens and piriform cortex. In the case of GABA, a significant increase in the local concentration of this amino acid was found in rats with stage 1 and 2 seizures in the prefrontal and entorhinal cortices and a decrease was present in amygdala. Kindling raised the local level of taurine in the entorhinal cortex (stage 1 and 2 seizures), amygdala, nucleus accumbens and piriform cortex (stage 5 seizures). These data confirm the conclusion that separate seizure circuitries in the forebrain structures mutually interact to facilitate and/or inhibit one another. Overall, these data suggest that there is a shift in the balance between neurotransmitters toward increased production of excitatory amino acids.

The role of interleukin-1β in the pentylenetetrazole-induced kindling of seizures, in the rat hippocampus.

Because the contribution of inflammatory mediators to seizure disorders is unclear, we investigated the changes in the expression of interleukin-1β (IL-β) and its receptor - IL-1 receptor type 1 (IL-1R1), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the rat hippocampus at different stages of pentylenetetrazole (PTZ)-induced kindling. The occurrence and progressive development of seizures were induced by repeated systemic administration of PTZ, a non-competitive antagonist of the γ-aminobutyric acid type A (GABAA) receptor at a subconvulsive dose of 30 mg/kg. We also examined the effects of continuous intracerebroventricular administration of IL-1β and lipopolysaccharide (LPS) in this model of epilepsy using subcutaneously implanted osmotic mini-pumps. We observed enhanced IL-1R1 expression in the dentate gyrus (DG) at different stages of kindling, whereas the elevated IL-1β level was distinctive to fully kindled seizures. We did not detect significant changes in the concentration of IL-6 or TNF-α throughout the kindling process. LPS accelerated transiently the process of kindling, while IL-1β showed a predisposition to delay kindling acquisition. Our study supports the concept of seizure-related modifications in brain cytokine production during epileptogenesis. Although some evidence indicates a proconvulsant property of IL-1β activity, it cannot be ruled out that the alterations in IL-1 system reflect the activation of endogenous protective mechanisms with respect to the kindling of seizures.

Is the interaction between fatty acids and tryptophan responsible for the efficacy of a ketogenic diet in epilepsy? The new hypothesis of action

The effects of a ketogenic diet in controlling seizure activity have been proven in many studies, although its mechanism of action remains elusive in many regards. We hypothesize that the ketogenic diet may exert its antiepileptic effects by influencing tryptophan (TRP) metabolism. The aim of this study was to investigate the influence of octanoic and decanoic fatty acids (FAs), the main components in the MCT diet (medium-chain triglyceride diet, a subtype of the ketogenic diet), on the metabolism of TRP, the activity of the kynurenic pathway and the concentrations of monoamines and amino acids, including branched-chain amino acids (BCAA) and aromatic amino acids (AAA) in rats. The acute effects of FA on the sedation index and hippocampal electrical after-discharge threshold were also assessed. We observed that intragastric administration of FA increased the brain levels of TRP and the central and peripheral concentrations of kynurenic acid (KYNA), as well as caused significant changes in the brain and plasma concentrations of BCAA and AAA. We found that the administration of FA clearly increased the seizure threshold and induced sedation. Furthermore, we have demonstrated that blocking TRP passage into the brain abolished these effects of FA but had no similar effect on the formation of ketone bodies. Given that FAs are major components of a ketogenic diet, it is suggested that the anticonvulsant effects of a ketogenic diet may be at least partly dependent on changes in TRP metabolism. We also propose a more general hypothesis concerning the intracellular mechanism of the ketogenic diet.

The role of IL-1β and glutamate in the effects of lipopolysaccharide on the hippocampal electrical kindling of seizures

In our study, we used rapid electrical hippocampal kindling and in vivo microdialysis methods to assess the involvement of inflammatory mediators: lipopolysaccharide (LPS) and proinflammatory interleukin-1β (IL-1β) in mechanisms of epileptogenesis. We observed, that both, LPS and IL-1β, administered into stimulated hippocampus, accelerated kindling process. LPS also increased the expression of IL-1β in stimulated hippocampus in kindled rats. In vivo acute LPS perfusion, via a microdialysis cannula implanted into the naïve rats hippocampus, produced an increase in extracellular glutamate release. We suppose, that particularly IL-1β action and increased glutamate concentration may significantly contribute to LPS effects on kindling development.

Altered expression of GABA-A receptor subunits in the hippocampus of PTZ-kindled rats

BACKGROUND Changes in the expression of the GABA-A receptor subunits involved in phasic and tonic inhibition have been studied in a wide spectrum of animal models of epilepsy. However, there is no exhaustive data regarding the pentylenetetrazole (PTZ) kindling model of epilepsy. METHODS The aim of our study was to analyse the hippocampal changes in the expression of GABA-A receptor subunits involved in phasic (α1, γ2) or tonic (α4 and δ) inhibition in rats subjected to the PTZ kindling using immunohistochemistry method as well as in animals subjected to a single injection of a subconvulsive (30mg/kg) or convulsive (55mg/kg) dose of PTZ. Moreover, the expression of GABA transporters (GAT-1 and GAT-3) was also assessed. RESULTS In kindled animals, we observed an increase in the expression of α1 (in CA1, DG (dentate gyrus) and CA3 regions) and γ2 (CA1 and CA3) subunits as well as in the expression of GAT-1 (CA1). On the other hand, the expression of the δ subunit in the DG was reduced. The single injection of PTZ at a dose of 30mg/kg increased the expression of the α4 subunit in the DG, while at a dose of 55mg/kg, PTZ increased the expression of the α1 and α4 subunits in the DG and reduced expression of the γ2 subunit in the CA1 and CA3 regions. CONCLUSIONS The pattern of changes observed in our study indicates that changes in tonic inhibition are involved in abnormal neuronal activity observed in PTZ model of epilepsy.

Differences in the dopaminergic reward system in rats that passively and actively behave in the Porsolt test

HighlightsPassive rats in the Porsolt test had more 50‐kHz USV episodes than active rats.Passive rats spend more time in amphetamine‐associated context.Stress increased 50‐kHz USV and reinforced amphetamine context in passive rats.Stressed passive rats had increased dopamine in the amygdala.Stress increased CART expression in the amygdala in passive rats. Abstract The aim of the study was to assess appetitive responses and central dopaminergic neurotransmission in passive and active rats divided according to their immobility time in the Porsolt swim test and exposed to restraint stress. Passive rats had more episodes of appetitive 50‐kHz ultrasonic vocalization (USV) during rat encounter after social isolation and spent significantly more time in the amphetamine‐associated context in conditioned place preference test, compared to active rats. Restraint stress decreased sucrose preference, but increased appetitive vocalization and reinforced the conditioned place preference only in passive animals that was associated with increased dopamine concentration in the amygdala. Restraint stress increased also the level of Cocaine‐ and Amphetamine Regulated Transcript (CART) peptide, a neuromodulator linked to dopamine neurotransmission, in the central nucleus of amygdala, while decreasing it the nucleus accumbens shell in passive rats. In the parvocellular region of paraventricular nucleus of the hypothalamus passive animals had a higher expression of CART compared to passive restraint rats and active control rats. The obtained results show that active and passive rats in the Porsolt test differ significantly in response to appetitive stimuli, which can be additionally changed under stress conditions. The underlying mechanisms are probably associated with differences in dopaminergic activity and CART signaling in reward system.