Neurobehavioral impairments in ciprofloxacin- treated osteoarthritic adult rats.

Background and purpose:

Ciprofloxacin (CIP) is a broad-spectrum antibiotic widely used in clinical practice to treat musculoskeletal infections. Fluoroquinolone-induced neurotoxic adverse events have been reported in a few case reports, all the preclinical studies on its neuropsychiatric side effects involved only healthy animals. This study firstly investigated the behavioral effects of CIP in an osteoarthritis rat model with joint destruction and pain, which can simulate inflammation-associated musculoskeletal pain. Furthermore, effects of CIP on regional brain-derived neurotrophic factor (BDNF) expression were examined given its major contributions to the neuromodulation and plasticity underlying behavior and cognition. 

Fourteen days after induction of chronic osteoarthritis, animals were administered vehicle, 33 mg/kg or 100 mg/kg CIP for five days intraperitoneally. Motor activity, behavioral motivation, and psychomotor learning were examined in a reward-based behavioral test (Ambitus) on Day 4 and sensorimotor gating by the prepulse inhibition test on Day 5. Thereafter, the prolonged BDNF mRNA and protein expression levels were measured in the hippocampus and the prefrontal cortex. 

CIP dose-dependently reduced both locomotion and reward-motivated exploratory activity, accompanied with impaired learning ability. In contrast, there were no significant differences in startle reflex and sensory gating among treatment groups; however, CIP treatment reduced motor activity of the animals in this test, too. These alterations were associated with reduced BDNF mRNA and protein expression levels in the hippocampus but not the prefrontal cortex. 

This study revealed the detrimental effects of CIP treatment on locomotor activity and motivation/learning ability during osteoarthritic condition, which might be due to, at least partially, deficient hippocampal BDNF expression and ensuing impairments in neural and synaptic plasticity.

Reinstating olfactory bulb-derived limbic gamma oscillations alleviates depression-like behavioral deficits in rodents.

Although the etiology of major depressive disorder remains poorly understood, reduced gamma oscillations is an emerging biomarker. Olfactory bulbectomy, an established model of depression that reduces limbic gamma oscillations, suffers from non-specific effects of structural damage. Here, we show that transient functional suppression of olfactory bulb neurons or their piriform cortex efferents decreased gamma oscillation power in limbic areas and induced depression-like behaviors in rodents. Enhancing transmission of gamma oscillations from olfactory bulb to limbic structures by closed-loop electrical neuromodulation alleviated these behaviors. By contrast, silencing gamma transmission by anti-phase closed-loop stimulation strengthened depression-like behaviors in naive animals. These induced behaviors were neutralized by ketamine treatment that restored limbic gamma power. Taken together, our results reveal a causal link between limbic gamma oscillations and depression-like behaviors in rodents. Interfering with these endogenous rhythms can affect behaviors in rodent models of depression, suggesting that restoring gamma oscillations may alleviate depressive symptoms.

Caffeine-Induced Acute and Delayed Responses in Cerebral Metabolism of Control and Schizophrenia-Like Wisket Rats.

Recently, morphological impairments have been detected in the brain of a triple-hit rat schizophrenia model (Wisket), and delayed depressive effects of caffeine treatment in both control and Wisket animals have also been shown. The aims of this study were to determine the basal and caffeine-induced acute (30 min) and delayed (24 h) changes in the cerebral 18fluorodeoxyglucose (18F-FDG) uptake by positron emission tomography (PET) in control and Wisket rats. No significant differences were identified in the basal whole-brain metabolism between the two groups, and the metabolism was not modified acutely by a single intraperitoneal caffeine (20 mg/kg) injection in either group. However, one day after caffeine administration, significantly enhanced 18F-FDG uptake was detected in the whole brain and the investigated areas (hippocampus, striatum, thalamus, and hypothalamus) in the control group. Although the Wisket animals showed only moderate enhancements in the 18F-FDG uptake, significantly lower brain metabolism was observed in this group than in the caffeine-treated control group. This study highlights that the basal brain metabolism of Wisket animals was similar to control rats, and that was not influenced acutely by single caffeine treatment at the whole-brain level. Nevertheless, the distinct delayed responsiveness to this psychostimulant in Wisket model rats suggests impaired control of the cerebral metabolism.

Wisket rat model of schizophrenia: Impaired motivation and, altered brain structure, but no anhedonia.

It is well-known that the poor cognition in schizophrenia is strongly linked to negative symptoms, including motivational deficit, which due to, at least partially, anhedonia. The goal of this study was to explore whether the schizophrenia-like Wisket animals with impaired motivation (obtained in the reward-based hole-board test), also show decreased hedonic behavior (investigated with the sucrose preference test). While neurochemical alterations of different neurotransmitter systems have been detected in the Wisket rats, no research has been performed on structural changes. Therefore, our additional aim was to reveal potential neuroanatomical and structural alterations in different brain regions in these rats. The rats showed decreased general motor activity (locomotion, rearing and exploration) and impaired task performance in the hole-board test compared to the controls, whereas no significant difference was observed in the sucrose preference test between the groups. The Wisket rats exhibited a significant decrease in the frontal cortical thickness and the hippocampal area, and moderate increases in the lateral ventricles and cell disarray in the CA3 subfield of hippocampus. To our knowledge, this is the first study to investigate the hedonic behavior and neuroanatomical alterations in a multi-hit animal model of schizophrenia. The results obtained in the sucrose preference test suggest that anhedonic behavior might not be involved in the impaired motivation obtained in the hole-board test. The neuropathological changes agree with findings obtained in patients with schizophrenia, which refine the high face validity of the Wisket model.

A Potential Interface between the Kynurenine Pathway and Autonomic Imbalance in Schizophrenia.

Schizophrenia is a neuropsychiatric disorder characterized by various symptoms including autonomic imbalance. These disturbances involve almost all autonomic functions and might contribute to poor medication compliance, worsened quality of life and increased mortality. Therefore, it has a great importance to find a potential therapeutic solution to improve the autonomic disturbances. The altered level of kynurenines (e.g., kynurenic acid), as tryptophan metabolites, is almost the most consistently found biochemical abnormality in schizophrenia. Kynurenic acid influences different types of receptors, most of them involved in the pathophysiology of schizophrenia. Only few data suggest that kynurenines might have effects on multiple autonomic functions. Publications so far have discussed the implication of kynurenines and the alteration of the autonomic nervous system in schizophrenia independently from each other. Thus, the coupling between them has not yet been addressed in schizophrenia, although their direct common points, potential interfaces indicate the consideration of their interaction. The present review gathers autonomic disturbances, the impaired kynurenine pathway in schizophrenia, and the effects of kynurenine pathway on autonomic functions. In the last part of the review, the potential interaction between the two systems in schizophrenia, and the possible therapeutic options are discussed.

Sleep-Wake Rhythm and Oscillatory Pattern Analysis in a Multiple Hit Schizophrenia Rat Model (Wisket).

Electroencephalography studies in schizophrenia reported impairments in circadian rhythm and oscillatory activity, which may reflect the deficits in cognitive and sensory processing. The current study evaluated the circadian rhythm and the state-dependent oscillatory pattern in control Wistar and a multiple hit schizophrenia rat model (Wisket) using custom-made software for identification of the artifacts and the classification of sleep-wake stages and the active and quiet awake substages. The Wisket animals have a clear light-dark cycle similar to controls, and their sleep-wake rhythm showed only a tendency to spend more time in non-rapid eye movement (NREM) and less in rapid eye movement (REM) stages. In spite of the weak diurnal variation in oscillation in both groups, the Wisket rats had higher power in the low-frequency delta, alpha, and beta bands and lower power in the high-frequency theta and gamma bands in most stages. Furthermore, the significant differences between the two groups were pronounced in the active waking substage. These data suggest that the special changes in the oscillatory pattern of this schizophrenia rat model may have a significant role in the impaired cognitive functions observed in previous studies.

Effects of D2 dopamine receptor activation in the ventral pallidum on sensory gating and food-motivated learning in control and schizophrenia model (Wisket) rats.

Dopamine D2 receptors (D2Rs) of the ventral pallidum (VP) play important role in motivational and learning processes, however, their potential role in triggering schizophrenic symptoms has not been investigated, yet. In the present experiments the effects of locally administered D2R agonist quinpirole were investigated on behavioral parameters related to sensorimotor gating, motor activity and food-motivated labyrinth learning. Two weeks after bilateral implantation of microcannulae into the VP, the acute (30 min) and delayed (3, 21 and 24 h) effects of quinpirole microinjection (1 µg/0.4 µL at both sides) were investigated in Wistar and schizophrenia model (Wisket substrain) rats in prepulse inhibition (PPI) and the reward-based Ambitus tests. Quinpirole administration did not modify the impaired sensorimotor gating in Wisket rats, but it led to significant deficit in Wistar animals. Regarding the locomotor activity in the Ambitus test, no effects of quinpirole were detected in either groups at the investigated time points. In contrast, quinpirole resulted in decreased exploratory and food-collecting activities in Wistar rats with 21 and 24 h delay. Though, impaired food-related motivation could be observed in Wisket rats, but quinpirole treatment did not result in further deterioration. In summary, our results showed that the VP D2R activation in Wistar rats induces symptoms similar to those observed in schizophrenia model Wisket rats. These data suggest that Wisket rats might have significant alterations in the functional activity of VP, which might be due to its enhanced dopaminergic activity.

Characterization of dopamine D2 receptor binding, expression and signaling in different brain regions of control and schizophrenia-model Wisket rats.

In previous studies we have shown that a three-hit animal model of schizophrenia (Wisket rat) has several behavioral impairments related to the disorder along with altered mu-opioid (MOP) and cannabinoid (CB1) receptor signaling. As the dopamine hypothesis of schizophrenia is central to research in the field, the goal of the present study was to investigate dopaminergic D2 receptor (D2R) functions (binding capacity, G-protein activation and expression) in several brain regions (hippocampus, prefrontal cortex, striatum, olfactory bulb, cerebellum, brainstem, cortex and diencephalon) of control (Wistar) and Wisket rats. It was found that the D2R mediated maximal activation of G-proteins was substantially higher in hippocampus, striatum and olfactory bulb membranes prepared from the Wisket than in control animals, which was accompanied with lower potency of the D2R-mediated G-protein activation. In contrast, enhanced potency was detected in the prefrontal cortex without changes in the maximal activation. In saturation binding assays the maximal binding capacity of D2Rs was higher in the model animals in cerebral cortex, striatum and lower in the brainstem, while no changes in the dissociation constant values were detected. The D2R mRNA expression showed a trend for greater level in the investigated areas, while the D2R protein expression was significantly higher of Wisket rats compared to Wistar animals in the hippocampus and in the prefrontal cortex but not in the cerebellum. This study proved that the Wisket animals show altered D2 receptor expression and function which might be related to the schizophrenia-like symptoms.

Synthesis, biochemical, pharmacological characterization and in silico profile modelling of highly potent opioid orvinol and thevinol derivatives.

Morphine and its derivatives play inevitably important role in the µ-opioid receptor (MOR) targeted antinociception. A structure-activity relationship study is presented for novel and known orvinol and thevinol derivatives with varying 3-O, 6-O, 17-N and 20-alkyl substitutions starting from agonists, antagonists and partial agonists. In vitro competition binding experiments with [3H]DAMGO showed low subnanomolar affinity to MOR. Generally, 6-O-demethylation increased the affinity toward MOR and decreased the efficacy changing the pharmacological profile in some cases. In vivo tests in osteoarthritis inflammation model showed significant antiallodynic effects of thevinol derivatives while orvinol derivatives did not. The pharmacological character was modelled by computational docking to both active and inactive state models of MOR. Docking energy difference for the two states separates agonists and antagonists well while partial agonists overlapped with them. An interaction pattern of the ligands, involving the interacting receptor atoms, showed more efficient separation of the pharmacological profiles. In rats, thevinol derivatives showed antiallodynic effect in vivo. The orvinol derivatives, except for 6-O-desmethyl-dihydroetorfin (2c), did not show antiallodynic effect.

Distinct changes in chronic pain sensitivity and oxytocin receptor expression in a new rat model (Wisket) of schizophrenia.

Clinical studies have shown that schizophrenia is accompanied by hypoalgesia. Accordingly, we have previously reported that a chronic schizophrenia-related rat substrain (Wisket) showed decreased acute heat pain sensitivity. The aim of the present study was to determine the mechanical pain sensitivity and the effects of opioid ligands in a chronic osteoarthritic pain model generated using Wisket rats. Our previous molecular biological studies indicated that the impairment in opioid and cannabinoid receptor functions observed in these animals did not explain their altered pain sensitivity. Therefore, we aimed to investigate another endogenous antinociceptive system, i.e., the oxytocinergic system (which is also implicated in schizophrenia) via the determination the brain-region specific oxytocin receptor mRNA expression in Wisket rats. Osteoarthritis was induced in male adult control Wistar rats without any interventions and in Wisket rats after juvenile social isolation and ketamine treatment. The degree of allodynia and the effects of systemic morphine or intrathecal endomorphin-1 administration were determined. Furthermore, the expression of the oxytocin receptor mRNA was assessed in different brain structures (prefrontal cortex, striatum, diencephalon, brainstem, and olfactory bulb). A lower degree of allodynia was observed in the Wisket group compared with control animals 1 and 2 weeks after the induction of osteoarthritis, which was accompanied by a comparable degree of edema. Systemically or intrathecally applied opioids caused similar time-response curves in both groups, with apparently shorter effects in Wisket animals. The expression of the oxytocin receptor mRNA was lower in most of the brain regions (with the exception of the diencephalon) investigated in Wisket rats vs. the control animals. In summary, both acute and chronic hypoalgesia (as nonspecific symptoms in patients with schizophrenia) can be simulated in Wisket animals as endophenotypes despite the impairment of the endogenous antinociceptive systems evaluated. Thus, this model might be an appropriate tool for further investigation of the molecular basis of altered pain perception in schizophrenia.

Kynurenines and the Endocannabinoid System in Schizophrenia: Common Points and Potential Interactions.

Schizophrenia, which affects around 1% of the world's population, has been described as a complex set of symptoms triggered by multiple factors. However, the exact background mechanisms remain to be explored, whereas therapeutic agents with excellent effectivity and safety profiles have yet to be developed. Kynurenines and the endocannabinoid system (ECS) play significant roles in both the development and manifestation of schizophrenia, which have been extensively studied and reviewed previously. Accordingly, kynurenines and the ECS share multiple features and mechanisms in schizophrenia, which have yet to be reviewed. Thus, the present study focuses on the main common points and potential interactions between kynurenines and the ECS in schizophrenia, which include (i) the regulation of glutamatergic/dopaminergic/γ-aminobutyric acidergic neurotransmission, (ii) their presence in astrocytes, and (iii) their role in inflammatory mechanisms. Additionally, promising pharmaceutical approaches involving the kynurenine pathway and the ECS will be reviewed herein.

Preparation of bivalent agonists for targeting the mu opioid and cannabinoid receptors.

In order to obtain novel pharmacological tools and to investigate a multitargeting analgesic strategy, the CB1 and CB2 cannabinoid receptor agonist JWH-018 was conjugated with the opiate analgesic oxycodone or with an enkephalin related tetrapeptide. The opioid and cannabinoid pharmacophores were coupled via spacers of different length and chemical structure. In vitro radioligand binding experiments confirmed that the resulting bivalent compounds bound both to the opioid and to the cannabinoid receptors with moderate to high affinity. The highest affinity bivalent derivatives 11 and 19 exhibited agonist properties in [35S]GTPγS binding assays. These compounds activated MOR and CB (11 mainly CB2, whereas 19 mainly CB1) receptor-mediated signaling, as it was revealed by experiments using receptor specific antagonists. In rats both 11 and 19 exhibited antiallodynic effect similar to the parent drugs in 20 µg dose at spinal level. These results support the strategy of multitargeting G-protein coupled receptors to develop lead compounds with antinociceptive properties.

Cognitive training improves the disturbed behavioral architecture of schizophrenia-like rats, "Wisket".

Translational schizophrenia research depends on the relevance of animal models supported by reliable tests. Human data suggest that the intensive cognitive training in schizophrenia improves the memory impairments and decreases the chance of acute psychiatric remission. Here we examined the effects of a 10-day long training session in the behavioral architecture of a new schizophrenia-like rat substrain (Wisket) in a narrow square corridor with food rewards (AMBITUS). The instrument was designed to model the natural environment of rats and enable the simultaneous recording of multiple behavioral parameters. For the compact visualization of differences between the Wisket and control animals in several parameters (behavioromics), color-coded grid plots were applied. The Wisket animals exhibited an altered pattern and/or amount of locomotion, exploratory and food collecting activity at the first few days, revealing impaired motivation, attention, anxiety and learning ability (face validity). Most of the parameters normalized with training, except for the decreased exploratory activity. This resembles the effects of cognitive behavioral therapy in human schizophrenics providing a significant support for the predictive validity of this substrain as an animal model of schizophrenia. This study also highlights the importance of behavior tests that investigate the egocentric learning ability during reward-based tasks.

Impaired pupillary control in "schizophrenia-like" WISKET rats.

Patients with schizophrenia show impairments in autonomic regulation, including pupillomotor control. The aim of this study was to explore the changes of pupillary light reflex in a new substrain (WISKET) with several schizophrenia-like alterations. Male WISKET rats housed individually (for four weeks) and treated with ketamine (for 3 × 5 days) after weaning and naive group-housed Wistar rats (controls) were involved in the study. The pupillary light reflex was studied in two series after sedation (diazepam) or anesthesia (chloral hydrate). Video recordings were evaluated with custom made video analyzer software. Several significant changes were observed between the two groups: the initial and minimum pupil diameters were greater, the degree of the constriction was lower, and the flatness of the curve and the total duration of constriction were shorter in the sedated WISKET rats. No other pupillary parameters (latency, amplitude and redilation) showed significant alterations. Chloral hydrate anesthesia prolonged the constriction and redilation processes compared to the sedated animals, and diminished the differences between the groups. In conclusion, WISKET rats showed disturbances in the pupillary light reflex, suggesting a general shift of autonomic balance towards a sympathetic predominance. The results provide further evidence to support the validity of WISKET rats as a complex, chronic animal model of schizophrenia.

Decreased CB receptor binding and cannabinoid signaling in three brain regions of a rat model of schizophrenia.

Schizophrenia is a serious mental health disorder characterized by several behavioral and biochemicel abnormalities. In a previous study we have shown that mu-opioid (MOP) receptor signaling is impaired in specific brain regions of our three-hit animal model of schizophrenia. Since the cannabinoid system is significantly influenced in schizophrenic patients, in the present work we investigated cannabinoid (CB) receptor binding and G-protein activation in cortical, subcortical and cerebellar regions of control and 'schizophrenic' rats. Cannabinoid agonist (WIN-55,212-2 mesylate) mediated G-protein activation was consistently decreased in all areas tested, and the difference was extremely significant in membranes prepared from the cerebellum. Interestingly, the cerebellar activity of WIN-55,212-2 stimulated G-proteins was substantially higher than those of cerebral cortex and subcortical region in control animals, indicating a primordial role of the cannabinoid system in the cerebellum. At the level of radioligand binding, the affinities of the CB receptors were also markedly decreased in the model animals. Capacity of the [3H]WIN-55,212-2 binding was only higher in the cerebellum of 'schizophrenic' model rats. Taken together, in all three brain areas of model rats both cannabinoid receptor binding and cannabinoid agonist-mediated G-protein activation were regularly decreased. Our results revealed that besides the opioids, the endocannabinoid - cannabis receptor system also shows impairment in our rat model, increasing its face validity and translational utility.

Electrophysiological alterations in a complex rat model of schizophrenia.

BACKGROUND: Psychiatric disorders are frequently accompanied by changes in brain electrical oscillations and abnormal auditory event related potentials. The goal of this study was to characterize these parameters of a new rat substrain showing several alterations related to schizophrenia. METHODS: Male rats of the new substrain, developed by selective breeding after combined subchronic ketamine treatment and postweaning social isolation, and naive Wistar ones group-housed without any interventions were involved in the present study. At the age of 3 months, animals were implanted with cortical electroencephalography electrodes. Auditory evoked potentials during paired-click stimuli and power of oscillation in different frequency bands were determined with and without acute ketamine (20mg/kg) treatment. RESULTS: Regarding the auditory evoked potentials, the latency of P2 was delayed and the amplitude of N1 peak was lower in the new substrain. The new substrain showed increased power of oscillations in the theta, alpha and beta bands, while decreased power was detected in delta and gamma2 bands (52-70Hz) compared with control animals. Acute ketamine treatment increased the gamma1 band (30-48Hz) power in both groups, while it elicited significant changes only in the new substrain in the total power and in alpha, beta and gamma2 bands. CONCLUSIONS: The validation of the translational utility of this new rat substrain by electrophysiological investigations revealed that these rats show abnormalities that may model a part of the neurophysiological deficits observed in schizophrenia.

Mu-Opioid (MOP) receptor mediated G-protein signaling is impaired in specific brain regions in a rat model of schizophrenia.

Schizophrenia is a complex mental health disorder. Clinical reports suggest that many patients with schizophrenia are less sensitive to pain than other individuals. Animal models do not interpret schizophrenia completely, but they can model a number of symptoms of the disease, including decreased pain sensitivities and increased pain thresholds of various modalities. Opioid receptors and endogenous opioid peptides have a substantial role in analgesia. In this biochemical study we investigated changes in the signaling properties of the mu-opioid (MOP) receptor in different brain regions, which are involved in the pain transmission, i.e., thalamus, olfactory bulb, prefrontal cortex and hippocampus. Our goal was to compare the transmembrane signaling mediated by MOP receptors in control rats and in a recently developed rat model of schizophrenia. Regulatory G-protein activation via MOP receptors were measured in [(35)S]GTPγS binding assays in the presence of a highly selective MOP receptor peptide agonist, DAMGO. It was found that the MOP receptor mediated activation of G-proteins was substantially lower in membranes prepared from the 'schizophrenic' model rats than in control animals. The potency of DAMGO to activate MOP receptor was also decreased in all brain regions studied. Taken together in our rat model of schizophrenia, MOP receptor mediated G-proteins have a reduced stimulatory activity compared to membrane preparations taken from control animals. The observed distinct changes of opioid receptor functions in different areas of the brain do not explain the augmented nociceptive threshold described in these animals.

Abnormal Motor Activity and Thermoregulation in a Schizophrenia Rat Model for Translational Science.

BACKGROUND: Schizophrenia is accompanied by altered motor activity and abnormal thermoregulation; therefore, the presence of these symptoms can enhance the face validity of a schizophrenia animal model. The goal was to characterize these parameters in freely moving condition of a new substrain of rats showing several schizophrenia-related alterations. METHODS: Male Wistar rats were used: the new substrain housed individually (for four weeks) and treated subchronically with ketamine, and naive animals without any manipulations. Adult animals were implanted with E-Mitter transponders intraabdominally to record body temperature and locomotor activity continuously. The circadian rhythm of these parameters and the acute effects of changes in light conditions were analyzed under undisturbed circumstances, and the effects of different interventions (handling, bed changing or intraperitoneal vehicle injection) were also determined. RESULTS: Decreased motor activity with fragmented pattern was observed in the new substrain. However, these animals had higher body temperature during the active phase, and they showed wider range of its alterations, too. The changes in light conditions and different interventions produced blunted hyperactivity and altered body temperature responses in the new substrain. Poincaré plot analysis of body temperature revealed enhanced short- and long-term variabilities during the active phase compared to the inactive phase in both groups. Furthermore, the new substrain showed increased short- and long-term variabilities with lower degree of asymmetry suggesting autonomic dysregulation. CONCLUSIONS: In summary, the new substrain with schizophrenia-related phenomena showed disturbed motor activity and thermoregulation suggesting that these objectively determined parameters can be biomarkers in translational research.

In vivo potency of different ligands on voltage-gated sodium channels.

The Ranvier nodes of thick myelinated nerve fibers contain almost exclusively voltage-gated sodium channels (Navs), while the unmyelinated fibers have several receptors (e.g., cannabinoid, transient receptor potential vanilloid receptor 1), too. Therefore, a nerve which contains only motor fibers can be an appropriate in vivo model for selective influence of Navs. The goals were to evaluate the potency of local anesthetic drugs on such a nerve in vivo; furthermore, to investigate the effects of ligands with different structures (arachidonic acid, anandamide, capsaicin and nisoxetine) that were proved to inhibit Navs in vitro with antinociceptive properties. The marginal mandibular branch of the facial nerve was explored in anesthetized Wistar rats; after its stimulation, the electrical activity of the vibrissae muscles was registered following the perineural injection of different drugs. Lidocaine, bupivacaine and ropivacaine evoked dose-dependent decrease in electromyographic activity, i.e., lidocaine had lower potency than bupivacaine or ropivacaine. QX-314 did not cause any effect by itself, but its co-application with lidocaine produced a prolonged inhibition. Nisoxetine had a very low potency. While anandamide and capsaicin in high doses caused about 50% decrease in the amplitude of action potential, arachidonic acid did not influence the responses. We proved that the classical local anesthetics have high potency on motor nerves, suggesting that this method might be a reliable model for selective targeting of Navs in vivo circumstances. It is proposed that the effects of these endogenous lipids and capsaicin on sensory fibers are not primarily mediated by Navs.

The inimitable kynurenic acid: the roles of different ionotropic receptors in the action of kynurenic acid at a spinal level.

Kynurenic acid (KYNA) is a neuroactive metabolite that interacts with NMDA, AMPA/kainate and alpha 7 nicotinic receptors. The goal of this study was to clarify the roles of these receptors in the action of KYNA at a spinal level by using highly specific receptor antagonists alone or in triple combinations. Chronic osteoarthritis-like joint pain was induced with monosodium-iodoacetate in male Wistar rats. Mechanical allodynia and motor function were quantified. In the first series we determined the dose-response and time course effects of intrathecally administered KYNA (10-100 µg), D-(-)-2-amino-5-phosphonopentanoic acid (AP5; an NMDA receptor antagonist; 10-200 µg), methyllycaconitine (MLA; an alpha 7 nicotinic receptor antagonist; 100-200 µg) and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzoquinoxaline-7-sulfonamide (NBQX; an AMPA/kainate receptor antagonist; 1-20 µg). In the second series, four different triple combinations of MLA, AP5 and NBQX were investigated. Intrathecal administration of KYNA caused a dose-dependent motor impairment and antinociception. The highly specific NMDA receptor antagonist AP5 caused a motor impairment and antinociception with lower potency. High doses of NBQX resulted in significant antinociception with a slight motor impairment, while only the highest dose of MLA gave rise to significant antinociception with a slight motor impairment. After the coadministration of these ligands as combinations, no potentiation was observed. It may be supposed that the effects of KYNA are primarily due to the inhibition of NMDA receptors at both glycine and phencyclidine (PCP) binding sites, and not to the interactions at the different ionotropic receptors, but the mechanisms behind its high bio-efficiency are still unknown.