Channel Blocker Lidocaine Research Articles

Lidocaine, MK-801, and MAC

Previous studies have found that the local anesthetic/sodium channel blocker lidocaine decreased MAC by maximum amounts approximately equal to the decreases produced by dizocilpine (MK-801), a N-methyl-d-aspartate (NMDA) receptor antagonist. Blockade of sodium channels by inhaled anesthetics has been suggested as a possible cause for impairment of transmission through NMDA receptors. We postulated that the net effect of lidocaine and MK-801 on MAC would be the same, albeit by affecting NMDA neurotransmission at different points. We measured the effect of various lidocaine infusions on the MAC of cyclopropane, halothane, isoflurane, and o-difluorobenzene in rats. We also measured the effect of concurrent lidocaine-MK-801 infusion on the MAC of isoflurane and o-difluorobenzene. Our data contradicted our predictions. (a) We found no limit to the effect of lidocaine infusion, in some cases finding that lidocaine, alone, produced immobility; (b) lidocaine infusion did not decrease the MAC of o-difluorobenzene differently from the MAC of other inhaled anesthetics; and (c) the addition of MK-801 equally affected the decrease in MAC produced by lidocaine infusion for isoflurane versus o-difluorobenzene. Lidocaine does not primarily decrease MAC by decreasing the release of glutamate from nerve terminals.

Limiting sarcolemmal Na+entry during resuscitation from ventricular fibrillation prevents excess mitochondrial Ca2+accumulation and attenuates myocardial injury

intracellular Na+ accumulation during ischemia and reperfusion leads to cytosolic Ca2+ overload through reverse-mode operation of the sarcolemmal Na+ -Ca2+ exchanger. Cytosolic Ca2+ accumulation promotes mitochondrial Ca2+ (Ca2+ m) overload, leading to mitochondrial injury. We investigated whether limiting sarcolemmal Na+ entry during resuscitation from ventricular fibrillation (VF) attenuates Ca2+ m overload and lessens myocardial dysfunction in a rat model of VF and closed-chest resuscitation. hearts were harvested from 10 groups of 6 rats each representing baseline, 15 min of untreated VF, 15 min of VF with chest compression given for the last 5 min (VF/CC), and 60 min postresuscitation (PR). VF/CC and PR included four groups each randomized to receive before starting chest compression the new NHE-1 inhibitor AVE4454B (1.0 mg/kg), the Na+ channel blocker lidocaine (5.0 mg/kg), their combination, or vehicle control. The left ventricle was processed for intracellular Na+ and Ca2+ m measurements. limiting sarcolemmal Na+ entry attenuated cytosolic Na+ increase during VF/CC and the PR phase and prevented Ca2+ m overload yielding levels that corresponded to 77% and 71% of control hearts at VF/CC and PR, without differences among specific Na+ -limiting interventions. Limiting sarcolemmal Na+ entry attenuated reductions in left ventricular compliance during VF and prompted higher mean aortic pressure (110 +/- 7 vs. 95 +/- 11 mmHg, P < 0.001) and higher cardiac work index (159 +/- 34 vs. 126 +/- 29 g x m x min(-1) x kg(-1), P < 0.05) with lesser increases in circulating cardiac troponin I at 60 min PR. Na+ -limiting interventions prevented excess Ca2+ m accumulation induced by ischemia and reperfusion and ameliorated myocardial injury and dysfunction.

Involvement of the Anterior Cingulate Cortex in the Expression of Remote Spatial Memory

Although the hippocampus plays a crucial role in the formation of spatial memories, as these memories mature they may become additionally (or even exclusively) dependent on extrahippocampal structures. However, the identity of these extrahippocampal structures that support remote spatial memory is currently not known. Using a Morris water-maze task, we show that the anterior cingulate cortex (ACC) plays a key role in the expression of remote spatial memories in mice. To first evaluate whether the ACC is activated after the recall of spatial memory, we examined the expression of the immediate early gene, c-fos, in the ACC. Fos expression was elevated after expression of a remote (1 month old), but not recent (1 d old), water-maze memory, suggesting that ACC plays an increasingly important role as a function of time. Consistent with the gene expression data, targeted pharmacological inactivation of the ACC with the sodium channel blocker lidocaine blocked expression of remote, but spared recent, spatial memory. In contrast, inactivation of the dorsal hippocampus disrupted expression of spatial memory, regardless of its age. We further showed that inactivation of the ACC blocked expression of remote spatial memory in two different mouse strains, after training with either a hidden or visible platform in a constant location, and using the AMPA receptor antagonist CNQX. Together, our data provide evidence that circuits supporting spatial memory are reorganized in a time-dependent manner, and establish that activity in neurons intrinsic to the ACC is critical for processing remote spatial memories.

Effects of medial amygdala inactivation on a panic-related behavior

In the last years, the role played by the medial nucleus of the amygdala (MeA) in the modulation of fear- and anxiety-related behaviors has been increasingly investigated. This nucleus plays an important role in the processing of predator odor-induced defensive reactions, i.e. freezing and risk-assessment behaviors. Immunohistochemical evidence also indicates that the MeA may be involved in the regulation of escape, a defensive behavior related to panic attacks. In this study, we further addressed this question by investigating the effects of the reversible inactivation of the nucleus on escape behavior generated in male Wistar rats by two different aversive stimuli, electrical stimulation of the dorsal periaqueductal gray matter (dPAG) and exposure to one of the open arms of the elevated T-maze. Results showed that intra-MeA administration of either the reversible sodium channel blocker lidocaine (34 nmol/0.2 μl) or the GABA A receptor agonist muscimol (0.22 nmol/0.2 μl) raised the threshold of aversive electrical stimulation, increasing the amount of current that applied to the dPAG evokes escape, an antiaversive effect. Local microinjection of muscimol (0.22 nmol/0.2 μl) inhibited escape behavior in the elevated T-maze, also suggesting an antiaversive effect. In this latter test, muscimol did not affect inhibitory avoidance, a behavior associated with generalized anxiety disorder. Muscimol effect in the elevated T-maze was independent of changes in general exploratory activity as measured in an open-field. Taken together, our data corroborate previous evidences suggesting that the MeA is involved in the modulation of escape. Dysfunction of this regulatory mechanism may be of relevance in the genesis/maintenance of panic disorder.

Ventricular Slices of Adult Mouse Hearts - a new Multicellular In Vitro Model for Electrophysiological Studies

Aim: We established a preparation of adult murineventricular slices suitable for electrophysiologicalrecordings as a new in vitro model of adultmyocardium with preserved in vivo tissue structure.Methods: Short axis slices (thickness: 150 µm) ofadult murine ventricles were prepared with amicrotome. Sharp glass electrodes were used formeasurements of action potentials (APs) atstimulation frequencies of 2 Hz and 10 Hz. Fieldpotential (FP) recordings by means of microelectrodearrays (MEAs) were performed to map excitationspread. Results: APs showed the characteristics ofadult murine ventricular APs: (i) a stable restingmembrane potential, (ii) a fast upstroke and (iii) afast phase 1 repolarization. Application of the Na+channel blocker lidocaine (30 µM) led to a declineof upstroke slope, amplitude and conduction speed.The unspecific K+ channel blocker 4-aminopyridine(5 mM) caused a prolongation of APD50. The excitationspread was homogenous throughout the ventricularwall. Conclusion: Adult murine ventricular slices areelectrophysiologically intact and respondphysiologically to cardioactive drugs. Thus, theyprovide a new multicellular in vitro model of adultcardiac tissue suitable for electrophysiologicalinvestigations, which in future could be used to studythe functional integration of stem cells transplantedin infarcted hearts in vivo.

Sleep-Dependent Plasticity Requires Cortical Activity

Recent findings in humans and animals suggest that sleep promotes synaptic plasticity, but the underlying mechanisms have not been identified. We have demonstrated recently an important role for sleep in ocular dominance (OD) plasticity, a classic form of in vivo cortical remodeling triggered by monocular deprivation (MD) during a critical period of development. The mechanisms responsible for the effects of sleep on OD plasticity are unknown but may depend on neuronal activity in the sleeping brain. We investigated the role of cortical activity in sleep-dependent plasticity by reversibly inactivating the sleeping visual cortex (V1) after a period of MD. Critical period cats were bilaterally implanted with cannulas in V1 and standard EEG/EMG electrodes for polysomnographic recording. After a period of MD, visual cortices were infused with the sodium channel blocker lidocaine in vehicle or vehicle only during sleep. A third group of cats served as sham controls and were infused with lidocaine outside of V1 (into the CSF). Both optical imaging of intrinsic cortical signals and microelectrode recordings showed that OD plasticity was significantly reduced in cats whose visual cortices were reversibly silenced during sleep. These findings demonstrate that the mechanisms governing this form of sleep-dependent plasticity require cortical activity. They provide an important insight into how sleep modifies synaptic circuitry by narrowing the range of possible candidate mechanisms to those that are activity dependent.

The Pentapeptide QYNAD Does Not Inhibit Neuronal Network Activity

Controversial data was published about the sodium channel-blocking effect of the endogenous pentapeptide QYNAD, which is elevated in patients with multiple sclerosis and Guillain-Barré-syndrome. In some experiments with single cells and nerve preparations QYNAD inhibited sodium currents to the same extent as the known sodium channel blocker lidocaine whereas in other laboratory testing QYNAD failed to show any effect at all. Micro-electrode arrays with cultured neuronal networks are highly suitable to determine neuroactive activity of applied substances. The impact on electrophysiological parameter changes was compared between QYNAD and the established sodium channel blockers lidocaine and tetrodotoxin (TTX). QYNAD did not alter network activity whereas the sodium channel blockers lidocaine (IC50 14.9 micorM) and tetrodotoxin (IC50 1.1 nM) reversibly decreased network activity in similar concentrations as in patch-clamp experiments. This decrease of spontaneous electrophysiological activity was achieved by prolonging the interburst-interval. Although QYNAD might have mild effects on single-cell sodium currents, there is no significant effect on neuronal network function. These results raise concerns about QYNAD exhibiting a relevant impact on functional disability of the central nervous system in patients.

Antiarrhythmic Engineering of Skeletal Myoblasts for Cardiac Transplantation

Skeletal myoblasts are an attractive cell type for transplantation because they are autologous and resistant to ischemia. However, clinical trials of myoblast transplantation in heart failure have been plagued by ventricular tachyarrhythmias and sudden cardiac death. The pathogenesis of these arrhythmias is poorly understood, but may be related to the fact that skeletal muscle cells, unlike heart cells, are electrically isolated by the absence of gap junctions. Using a novel in vitro model of myoblast transplantation in cardiomyocyte monolayers, we investigated the mechanisms of transplant-associated arrhythmias. Cocultures of human skeletal myoblasts and rat cardiomyocytes resulted in reentrant arrhythmias (spiral waves) that reproduce the features of ventricular tachycardia seen in patients receiving myoblast transplants. These arrhythmias could be terminated by nitrendipine, an l-type calcium channel blocker, but not by the Na channel blocker lidocaine. Genetic modification of myoblasts to express the gap junction protein connexin43 decreased arrhythmogenicity in cocultures, suggesting a specific means for increasing the safety (and perhaps the efficacy) of myoblast transplantation in patients.

Intravenous Lidocaine Relieves Spinal Cord Injury Pain

Neuropathic pain in spinal cord injury is a common challenging therapeutic condition. The current study examines the analgesic effect of the sodium channel blocker lidocaine on neuropathic pain in patients with spinal cord injury and the predictive role of concomitant evoked pain on pain relief with lidocaine. Twenty-four spinal cord injury patients with neuropathic pain at or below the level of injury were randomized and completed a double-blind crossover trial of 5 mg/kg lidocaine and placebo infused over 30 min. Twelve patients reported evoked pain, and 12 patients had no evoked pain. Spontaneous and evoked pains were assessed using a visual analog scale and quantitative sensory testing. Lidocaine significantly reduced spontaneous pain in all patients (P < 0.01) and in each of the two groups with (P < 0.01) and without (P = 0.048) evoked pain, with no difference in number of responders (pain reduction > or = 33%) between the patients with (n = 6) and without (n = 5) evoked pain. Lidocaine significantly relieved both at-level and below-level neuropathic pain and decreased brush-evoked dysesthesia but not cold allodynia, pinprick hyperalgesia, or pain evoked by repetitive pinprick. Lidocaine reduced neuropathic pain at and below the level of injury irrespective of the presence or absence of evoked pain. Results are consistent with a central-acting effect of sodium channel blockers acting on neuronal hyperexcitability. Agents (such as anticonvulsants or antiarrhythmics) with sodium channel-blocking properties may be a treatment option for spinal cord injury pain.

Polarized arrest with warm or cold adenosine/lidocaine blood cardioplegia is equivalent to hypothermic potassium blood cardioplegia

Hypothermic depolarizing hyperkalemic (K + 20 mEq/L) blood cardioplegia is the "gold standard" in cardiac surgery. K + has been associated with deleterious consequences, eg, intracellular calcium overload. This study tested the hypothesis that elective arrest in a polarized state with adenosine (400 micromol/L via adenosine triphosphate-sensitive potassium channel opening) and the Na + channel blocker lidocaine (750 micromol/L) as the arresting agents in blood cardioplegia provides cardioprotection comparable to standard hypothermic K + -blood cardioplegia. Anesthetized dogs were placed on cardiopulmonary bypass and assigned to 1 of 3 groups receiving antegrade cardioplegia delivered every 20 minutes for 1 hour of arrest: cold (10 degrees C) K + -blood cardioplegia (n = 6), cold (10 degrees C) adenosine/lidocaine blood cardioplegia (n = 6), or warm (37 degrees C) adenosine/lidocaine blood cardioplegia (n = 6). After an hour of arrest, cardiopulmonary bypass was discontinued, and reperfusion was continued for 120 minutes. Time to arrest was longer with cold and warm adenosine/lidocaine blood cardioplegia (175 +/- 19 seconds and 143 +/- 19 seconds, respectively) compared with K + -blood cardioplegia (27 +/- 2 seconds; P < .001). Postcardioplegia left ventricular systolic function (slope of the end-systolic pressure/dimension relationship) was comparable among the 3 groups (K + -blood cardioplegia, 15.2 +/- 2.1 mm Hg/mm; cold adenosine/lidocaine blood cardioplegia, 15.9 +/- 3.4 mm Hg/mm; warm adenosine/lidocaine blood cardioplegia, 14.1 +/- 2.8 mm Hg/mm; P = .90). Plasma creatine kinase activity in cold and warm adenosine/lidocaine blood cardioplegia was similar to that in K + -blood cardioplegia at 120 minutes of reperfusion (cold adenosine/lidocaine blood cardioplegia, 11.5 +/- 2.1 IU/g protein; warm adenosine/lidocaine blood cardioplegia, 10.1 +/- 0.9 IU/g protein; K + -blood cardioplegia, 7.6 +/- 0.8 IU/g protein; P = .17). Postcardioplegia coronary artery endothelial function was preserved in all groups. Intermittent polarized arrest with warm or cold adenosine/lidocaine blood cardioplegia provided the same degree of myocardial protection as intermittent hypothermic K + -blood cardioplegia in normal hearts.

Instrumental Learning Within the Rat Spinal Cord: Localization of the Essential Neural Circuit.

Following spinal transection of the upper thoracic spinal cord, male Sprague-Dawley rats given legshock whenever a hindlimb is extended learn to maintain the leg in a flexed position. The region of the cord that mediates this instrumental learning was isolated using neuroanatomical tracing, localized infusion of lidocaine, and surgical transections. DiI and Fluoro-Gold microinjection at the site of shock application labeled motor neuron bodies of lamina IX in the lower lumbar region. Local application of the Na-super++ channel blocker lidocaine disrupted learning when it was applied over a region extending from the lower lumbar (L3) to upper sacral (S2) cord. The drug had no effect rostral or caudal to this region. Surgical transections as low as L4 had no effect on learning. Learning also survived a dual transection at L4 and S3, but not L4 and S2. The results suggest that the essential neural circuit lies between L4 and S3.

Pharmacological characterisation of the rat brachial plexus avulsion model of neuropathic pain

Recently, our laboratory has proposed the avulsion of rat brachial plexus as a new and reliable model for the study of neuropathic pain. In this model, the neuropathy can be detected even at distant sites from the injury, both in ipsilateral and contralateral hindpaws. The purpose of this study was to pharmacologically characterise this behavioural model of persistent peripheral neuropathic pain by assessing the effects of several analgesic drugs currently used in clinical practice. For this purpose, the effects of these drugs on the mechanical and cold allodynia were analysed 20–40 days after rat brachial plexus avulsion. Injection of saline, administered by the same route as the other drugs, did not significantly affect the nociceptive threshold either in sham-operated or in neuropathic rats. However, administration of the opioid analgesic morphine (5 mg/kg, s.c.), the α 2 adrenoceptor agonist clonidine (300 μg/kg, i.p.), the NMDA receptor antagonist ketamine (25 mg/kg, i.p.) or the anticonvulsant drug gabapentin (70 mg/kg, p.o.) consistently reduced both mechanical and cold allodynia following avulsion of rat brachial plexus. The administration of the selective COX-2 inhibitor celecoxib (10 mg/kg, p.o.) blocked mechanical allodynia, but not cold allodynia, whereas the sodium channel blocker lidocaine (40 mg/kg, i.p.) attenuated only cold allodynia. The non-steroidal anti-inflammatory drug diclofenac (100 mg/kg, i.p.), the steroidal anti-inflammatory dexamethasone (1.5 mg/kg, i.p.) and the antidepressant imipramine (10 mg/kg, i.p.) all failed to significantly attenuate both mechanical and cold allodynia in the rats following avulsion of brachial plexus. These findings suggest that avulsion-associated mechanical and cold allodynia, two classic signs of persistent neuropathic pain, were consistently prevented by several analgesics currently available in clinical practice, namely morphine, clonidine, ketamine and gabapentin, and to a lesser extent by celecoxib and lidocaine. Therefore, this new proposed model of persistent nociception seems to be suitable for the study of the underlying mechanisms involved in neuropathic pain and for the identification of potential clinically relevant drugs to treat this aspect of peripheral neuropathy.

Interaction between perirhinal and medial prefrontal cortex is required for temporal order but not recognition memory for objects in rats.

The present study investigated the roles of the perirhinal cortex, medial prefrontal cortex, and intrahemispheric interactions between them in recognition and temporal order memory for objects. Experiment 1 assessed the effects of bilateral microinfusions of the sodium channel blocker lidocaine into either the anterior perirhinal or medial prefrontal cortex immediately before memory testing in a familiarity discrimination task and a recency discrimination task, both of which involved spontaneous exploration of objects. Inactivation of the perirhinal cortex disrupted performance in both tasks, whereas inactivation of the medial prefrontal cortex disrupted performance in the recency, but not the familiarity, discrimination task. In a second experiment, the importance of intrahemispheric interactions between these structures in temporal order memory were assessed by comparing the effects of unilateral inactivation of either structure alone with those of crossed unilateral inactivation of both structures on the recency discrimination task. Crossed unilateral inactivation of both structures produced a significant impairment, whereas inactivation of either structure alone produced little or no impairment. Collectively, these findings suggest that the perirhinal cortex, but not the medial prefrontal cortex, contributes to retrieval of information necessary for long-term object recognition, whereas both structures, via intrahemispheric interactions between them, contribute to retrieval of information necessary for long-term object temporal order memory. These data are consistent with models in which attributed information is stored in posterior cortical sites and supports lower-order mnemonic functions (e.g., recognition memory) but can also be retrieved and further processed via interactions with the prefrontal cortex to support higher-order mnemonic functions (e.g., temporal order memory).

Dorsal Horn Neurons Firing at High Frequency, But Not Primary Afferents, Release Opioid Peptides that Produce μ-Opioid Receptor Internalization in the Rat Spinal Cord

To determine what neural pathways trigger opioid release in the dorsal horn, we stimulated the dorsal root, the dorsal horn, or the dorsolateral funiculus (DLF) in spinal cord slices while superfusing them with peptidase inhibitors to prevent opioid degradation. Internalization of mu-opioid receptors (MOR) and neurokinin 1 receptors (NK1R) was measured to assess opioid and neurokinin release, respectively. Dorsal root stimulation at low, high, or mixed frequencies produced abundant NK1R internalization but no MOR internalization, indicating that primary afferents do not release opioids. Moreover, capsaicin and NMDA also failed to produce MOR internalization. In contrast, dorsal horn stimulation elicited MOR internalization that increased with the frequency, being negligible at <10 Hz and maximal at 500 Hz. The internalization was abolished by the MOR antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP), in the presence of low Ca2+ and by the Na+ channel blocker lidocaine, confirming that it was caused by opioid release and neuronal firing. DLF stimulation in "oblique" slices (encompassing the DLF and the dorsal horn of T11-L4) produced MOR internalization, but only in areas near the stimulation site. Moreover, cutting oblique slices across the dorsal horn (but not across the DLF) eliminated MOR internalization in areas distal to the cut, indicating that it was produced by signals traveling in the dorsal horn and not via the DLF. These findings demonstrate that some dorsal horn neurons release opioids when they fire at high frequencies, perhaps by integrating signals from the rostral ventromedial medulla, primary afferents, and other areas of the spinal cord.

Neurokinin release produced by capsaicin acting on the central terminals and axons of primary afferents: relationship with n-methyl- d-aspartate and gaba b receptors

Capsaicin stimulates neurokinin release in the spinal cord when applied both centrally and peripherally. To determine whether these two actions have different mechanisms, we measured neurokinin 1 receptor (NK1R) internalization in rat spinal cord slices elicited by incubating the whole slice or just the dorsal root with capsaicin. NK1R internalization produced by incubating the slices with capsaicin was abolished by the NK1R antagonist RP-67580, by the vanilloid receptor 1 (VR1) antagonist capsazepine, and by eliminating Ca 2+ from the medium, but was not affected by the Na + channel blocker lidocaine. Therefore, the internalization was due to neurokinin release mediated by Ca 2+ entry through VR1 receptors, but did not require the firing of action potentials. Incubating the root with capsaicin produced NK1R internalization in the ipsilateral dorsal horn that was abolished when capsazepine or lidocaine was included in, or when Ca 2+ was omitted from, the medium surrounding the root. Therefore, the internalization was mediated by Ca 2+ entry in the axons through VR1, and required firing of action potentials. The efficacy of capsaicin when applied to the root (36±3%) was lower than when applied to the slice (91±3%), but its potency was the same (0.49 μM and 0.37 μM, respectively). We also investigated whether presynaptic N-methyl- d-aspartate (NMDA) and GABA B receptors modulate these two actions of capsaicin. Neither the NMDA receptor blocker MK-801 nor the GABA B agonist baclofen decreased NK1R internalization produced by 1 μM capsaicin applied to the slices, but they inhibited the internalization produced by 0.3 μM capsaicin applied to the slices or 1 μM capsaicin applied to the root. Therefore, capsaicin can produce neurokinin release from primary afferents 1) by a direct action on their central terminals and 2) by increasing the firing of action potentials on their axons. The first effect largely bypasses other modulatory mechanism, but the second does not.

Tedisamil and lidocaine enhance each other's antiarrhythmic activity against ischaemia-induced arrhythmias in rats.

1. Combinations of the action potential-widening drug tedisamil (Class III antiarrhythmic activity), and the inactivated state sodium channel blocker lidocaine (Class Ib antiarrhythmic activity) were assessed for antiarrhythmic actions in a rat model of ischaemia-induced arrhythmias and for electrophysiological actions in normal rat myocardial tissue. 2. Both tedisamil and lidocaine dose-dependently suppressed ischaemia-induced arrhythmias. The ED(50) values were 3.0+/-1.3 and 4.9+/-0.6 micro mol kg(-1) min(-1), respectively. 3. Combinations of the two drugs acted synergistically such that the ED(50) for tedisamil was reduced to 0.8+/-0.2 micro mol kg(-1) min(-1) in the presence of 2 micro mol kg(-1) min(-1) lidocaine. Similarly, the ED(50) for lidocaine was reduced to 0.7+/-0.2 micro mol kg(-1) min(-1) in the presence of 2 micro mol kg(-1) min(-1) tedisamil (both P<0.05). 4. In a separate series of experiments in which normal ventricular tissue was electrically stimulated, 2 micro mol kg(-1) min(-1) lidocaine produced a leftward shift in the dose-response curve for tedisamil's effect on effective refractory period (P<0.05). This dose of lidocaine had no effect on its own. These data indicate that the synergistic actions of combinations of tedisamil and lidocaine were mediated, at least in part, by extension of effective refractory period in normal myocardial tissue. 5. In contrast to the strategy of developing drugs that are selective for a single electrophysiological mechanism, the results of the present study suggest that effective antiarrhythmic drugs might be developed by optimising the combination of two complimentary electrophysiological mechanisms (i.e., action potential-prolonging activity and inactivated state sodium channel blockade).

Independent modulation of basal and feeding-evoked dopamine efflux in the nucleus accumbens and medial prefrontal cortex by the central and basolateral amygdalar nuclei in the rat

Interactions of the central and basolateral nuclei of the amygdala with the mesocorticolimbic dopamine system are implicated in the acquisition and performance of conditioned responses for food reward. This study investigated whether dopamine transmission in the nucleus accumbens and the medial prefrontal cortex of the rat is influenced by the amygdala and if so, to assess the significance of the interaction in free feeding of a palatable food. To this end, we examined the effects of reverse-dialysis of the sodium channel blocker lidocaine into either the central or basolateral on dopamine efflux in the nucleus accumbens and the medial prefrontal cortex as determined by microdialysis and high-pressure liquid chromatography with electrochemical detection. The present results revealed for the first time that inactivation of the central decreased basal levels of dopamine efflux in the nucleus accumbens, but not in the medial prefrontal cortex. Furthermore, administration of lidocaine into the central significantly attenuated feeding-evoked increases in dopamine efflux in both terminal regions. These neurochemical effects were accompanied by feeding-related behaviours akin to the Klüver-Bucy syndrome. In contrast, inactivation of the basolateral affected neither food intake nor dopamine efflux in the nucleus accumbens, but triggered dramatic long-lasting oscillations in dopamine efflux in the medial prefrontal cortex, irrespective of whether food was presented or not. Overall, these findings indicate that the central and basolateral independently modulate dopamine transmission in both terminal regions of the mesocorticolimbic dopamine system. The central, in particular, and its influence on the dopamine system, may be involved in the regulation of food intake.

Additive stimulatory effect of extracellular calcium and potassium on non-transferrin ferric iron uptake by HeLa and K562 cells

We studied the effects of Ca 2+ and K + on non-transferrin iron uptake from ferric citrate complex by HeLa and K562 cells. Uptake experiments in Na-HEPES buffer (137 mM NaCl, 4 mM KCl) showed that extracellular Ca 2+ stimulated the iron uptake. The rate of iron uptake in 4 mM Ca 2+ was about 3–5 times higher than without Ca 2+. The iron uptake in K-HEPES buffer (68 mM NaCl, 75 mM KCl) with a high K + level was transiently stimulated during the first 10 min. The rate of iron uptake for 0.4 mM Ca 2+ was approximately 3 times higher in K-HEPES buffer than in Na-HEPES buffer. The calcium channel blockers verapamil (50 μM) and nifedipine (5 μM) had no effect on the uptake either in control Na-HEPES buffer or after K + stimulation in K-HEPES buffer. The sodium channel blocker lidocaine (50 μM) also had no effect on the uptake of iron in Na-HEPES buffer as well as after K + stimulation. Furthermore, the iron uptake was not significantly affected when Na + in the Na-HEPES and K-HEPES buffers was replaced by isotonic saccharose. We conclude that extracellular calcium per se, and not intracellular calcium or Ca 2+ transport, stimulates ferric iron uptake by both HeLa and K562 cells. A high level of extracellular K + also stimulates the uptake, probably via cell membrane depolarization. Na + is not involved in these stimulations of iron uptake. The transient K + effect and continuous Ca 2+ effect seem to be additive.

Pharmacological involvement of the calcium channel blocker flunarizine in dopamine transmission at the striatum

Single intrastriatal microinjections of 25, 50 and 100 nmol/μl of flunarizine in normal rats produced a dose-dependent turning behavior toward the injected side when they were challenged with apomorphine (1 mg/kg, s.c). This effect was seen at 1, 3 and 7 days following administration of the high dose of flunarizine, but had subsided by 24 h after administration of the intermediate dose; the low dose was ineffective. However, intrastriatal injection of the high dose of flunarizine resulted in a local lesion and thereafter this dose was not used. A similar dose-response relationship was determined for nifedipine, an L-type calcium channel antagonist. Injection of this antagonist did not result in apomorphine-elicited rotational behavior, reflecting its lack of antidopaminergic action. Intrastriatal injections of haloperidol (5 μg/μl), an antagonist of dopamine D 2 receptors, or the sodium channel blocker lidocaine (40 μg/μl), were given in order to compare their effects to those observed with flunarizine. Intracerebral injection of haloperidol produced ipsilateral turning in response to systemic administration of apomorphine given 60 min after. The same response was obtained with the injection of apomorphine 10 min after the injection of intracerebral lidocaine. This effect was no longer apparent 24 h after the microinjection of haloperidol and 60 min after the injection of lidocaine. In rats rendered hemiparkinsionian by lesioning the nigrostriatal pathway with 6OHDA, intrastriatal microinjection of flunarizine (50 nmol/μl) significantly reduced apomorphine (0.2 mg/kg, s.c.)-elicited turning behavior towards the non-lesioned side. These results suggest an antidopaminergic effect of flunarizine mediated by antagonistic action of post-synaptic striatal dopamine receptors. However, an action of the drug on sodium channels may not be ruled out. These studies offer additional supporting evidence for the induction or aggravation of extrapyramidal side-effects in patients receiving flunarizine.

Preliminary study on the suitability of a pharmacological bio-assay based on cardiac myocytes cultured over microfabricated microelectrode arrays

There are a range of techniques that can be used to assay bioactive compound. One potentially promising technique is a system consisting of microfabricated extracellular recording devices over which electrogenic cells can be grown. To date, research in this area has concentrated on the use of neurons as an electrogenic cell type. However, these cells have limitations. Only small extracellular potentials have been recorded from mammalian neurons cultured over microfabricated electrode arrays. Although such potentials may be of use in assays examining the effects of bio-active compound analogues on firing frequency, they are of little use for more detailed pharmacological studies involving analyses of signal shape. What is required is a system from which much larger extracellular potentials can be recorded. This preliminary study reports on a system based on cardiac myocytes cultured over microfabricated metal microelectrode arrays, from which potentials with a mean amplitude of 16.9 microV can be reliably recorded, which can be reversibly blocked with mumoll-1 concentrations of the sodium ion channel blocker lidocaine. Less common potentials with amplitudes of up to 3.5 mV were also recorded. It is demonstrated that cardiac myocytes cultured over microfabricated micro-electrode arrays can be used in assays of cardioactive compound analogues.