L. Ver Donck

Robust anti‐arrhythmic efficacy of verapamil and flunarizine against dofetilide‐induced TdP arrhythmias is based upon a shared and a different mode of action

BACKGROUND AND PURPOSE The high predisposition to Torsade de Pointes (TdP) in dogs with chronic AV‐block (CAVB) is well documented. The anti‐arrhythmic efficacy and mode of action of Ca2+ channel antagonists, flunarizine and verapamil against TdP were investigated.

Sarcolemma-bound calcium. Its importance for cell viability

We report the presence of a sarcolemma-associated Ca2+-pool in the intact myocardium and isolated ventricular myocytes of the rat. Ca2+-deposits, which are visualized in the electron microscope as 20 nm thick particles, could be demonstrated when fixation of the tissue was performed in the presence of high inorganic phosphate and most probably represent stable Ca2+-acidic phospholipid-phosphate complexes. Various pathophysiological conditions all leading to intracellular Ca2+-overload and compromising myocardial cell viability were imposed and the distribution of Ca2+ was assessed. It was found that in all these conditions cellular Ca2+-overload was preceded or at least accompanied by a loss of sarcolemma-associated Ca2+-deposits. It is concluded that this Ca2+, possibly bound to acidic phospholipids of the sarcolemmal bilayer, plays a role in the maintenance of sarcolemmal integrity. These cytological observations support a concept previously proposed by Langer and his group on the controlling role of membrane Ca2+ in the overall cellular Ca2+-homeostasis.

Blockade of the metabotropic glutamate (mGluR2) modulates arousal through vigilance states transitions: evidence from sleep-wake EEG in rodents.

Accumulating data continue to support the therapeutic potential of glutamate metabotropic (mGluR2) receptors for treatment of psychiatric disorders such as depression, anxiety and schizophrenia. Glutamate neurotransmission is an integral component of sleep-wake mechanisms, which have translational relevance to assess on-target activity of drugs. Here, we investigated the influence of mGluR2 inactivation upon sleep-wake electroencephalogram (EEG) in rodents. Rats were administered with vehicle, the specific mGluR2 antagonist LY341495 (2.5, 5, 10mg/kg) or negative allosteric modulator (NAM) Ro-4491533 (2.5, 10 and 40 mg/kg) at lights onset. mGluR2 (-/-) mice were used to confirm the selectivity of functional response. Both LY341495 and Ro-4491533 induced an immediate and endured desynchronized cortical activity during 3-6h associated with enhanced theta and gamma oscillations and depressed slow oscillations during sleep. The arousal-promoting effect is consistent with the marked lengthening of sleep onset latency, an increased number of state transitions from light sleep to waking and the gradual increase in homeostatic compensatory sleep. The arousal response to mGluR2 blockade was not accompanied by sharp rebound hypersomnolence as found with the classical psycho-stimulant amphetamine. mGluR2 (-/-) mice and their WT littermates exhibited similar sleep-wake phenotype, while Ro-4491533 (40 mg/kg) enhanced waking associated with increased locomotor activity and body temperature in WT but not in mGluR2 (-/-) mice, which confirm the role of mGluR2 inactivation in the arousal response. Our results lend support for a role of mGluR2 blockade in promoting cortical arousal associated with theta/gamma oscillations as well as high thresholds transitions from sleep to waking.

Subchronic memantine induced concurrent functional disconnectivity and altered ultra-structural tissue integrity in the rodent brain: revealed by multimodal MRI

BackgroundAn effective NMDA antagonist imaging model may find key utility in advancing schizophrenia drug discovery research. We investigated effects of subchronic treatment with the NMDA antagonist memantine by using behavioural observation and multimodal MRI.MethodsPharmacological MRI (phMRI) was used to map the neuroanatomical binding sites of memantine after acute and subchronic treatment. Resting state fMRI (rs-fMRI) and diffusion MRI were used to study the changes in functional connectivity (FC) and ultra-structural tissue integrity before and after subchronic memantine treatment. Further corroborating behavioural evidences were documented.ResultsDose-dependent phMRI activation was observed in the prelimbic cortex following acute doses of memantine. Subchronic treatment revealed significant effects in the hippocampus, cingulate, prelimbic and retrosplenial cortices. Decreases in FC amongst the hippocampal and frontal cortical structures (prelimbic, cingulate) were apparent through rs-fMRI investigation, indicating a loss of connectivity. Diffusion kurtosis MRI showed decreases in fractional anisotropy and mean diffusivity changes, suggesting ultra-structural changes in the hippocampus and cingulate cortex. Limited behavioural assessment suggested that memantine induced behavioural effects comparable to other NMDA antagonists as measured by locomotor hyperactivity and that the effects could be reversed by antipsychotic drugs.ConclusionOur findings substantiate the hypothesis that repeated NMDA receptor blockade with nonspecific, noncompetitive NMDA antagonists may lead to functional and ultra-structural alterations, particularly in the hippocampus and cingulate cortex. These changes may underlie the behavioural effects. Furthermore, the present findings underscore the utility and the translational potential of multimodal MR imaging and acute/subchronic memantine model in the search for novel disease-modifying treatments for schizophrenia.

Subchronic treatment with phencyclidine in adolescence leads to impaired exploratory behavior in adult rats without altering social interaction or N-methyl-D-aspartate receptor binding levels

Although both the onset of schizophrenia and human phencyclidine (PCP) abuse typically present within the interval from adolescence to early adulthood, the majority of preclinical research employing the PCP model of schizophrenia has been conducted on neonatal or adult animals. The present study was designed to evaluate the behavioral and neurochemical sequelae of subchronic exposure to PCP in adolescence. Male 35–42‐day‐old Sprague Dawley rats were subcutaneously administered either saline (10 ml · kg−1) or PCP hydrochloride (10 mg · kg−1) once daily for a period of 14 days (n = 6/group). The animals were allowed to withdraw from treatment for 2 weeks, and their social and exploratory behaviors were subsequently assessed in adulthood by using the social interaction test. To examine the effects of adolescent PCP administration on the regulation of N‐methyl‐D‐aspartate receptors (NMDARs), quantitative autoradiography was performed on brain sections of adult, control and PCP‐withdrawn rats by using 20 nM 3H‐MK‐801. Prior subchronic exposure to PCP in adolescence had no enduring effects on the reciprocal contact and noncontact social behavior of adult rats. Spontaneous rearing in response to the novel testing arena and time spent investigating its walls and floor were reduced in PCP‐withdrawn animals compared with control. The long‐term behavioral effects of PCP occurred in the absence of persistent deficits in spontaneous locomotion or self‐grooming activity and were not mediated by altered NMDAR density. Our results document differential effects of adolescent PCP administration on the social and exploratory behaviors of adult rats, suggesting that distinct neurobiological mechanisms are involved in mediating these behaviors.

Effects of lidoflazine and mioflazine against potassium and veratrine induced shape changes in isolated rat cardiac myocytes

SummaryThe protective effects of lidoflazine and mioflazine against shape changes in isolated rat cardiac myocytes induced by depolarizing concentrations of potassium and veratrine have been examined. Myocardial cells, isolated from adult rat hearts and plated in Petri-dishes, yielded a population of nearly 100% rod-shaped calcium-tolerant myocytes. Addition of veratrine or potassium resulted in a calcium-dependent cell shortening and finally rounding up of nearly all cells.Ultrastructurally, the shape changes were accompanied by a complete loss of calcium associated with the sarcolemmal and T-tubular bilayer. Calcium deposits accumulated in the mitochondria, indicating intracellular calcium overload. Pretreatment of the myocytes with lidoflazine or mioflazine (10−7-10−5 M) dose-dependently increased the number of remanining rod-shaped cells after potassium or veratrine addition. Such rod-shaped cells retained a normal pattern of calcium distribution along the sarcolemma and T-tubuli with no evidence of mitochondrial calcium overload. The protective effects of lidoflazine and mioflazine are explained in terms of preserving sarcolemmal integrity, whereby excessive calcium influx and subsequent cytosolic calcium overload could be prevented.

Panic results in unique molecular and network changes in the amygdala that facilitate fear responses

Recurrent panic attacks (PAs) are a common feature of panic disorder (PD) and post-traumatic stress disorder (PTSD). Several distinct brain regions are involved in the regulation of panic responses, such as perifornical hypothalamus (PeF), periaqueductal gray, amygdala and frontal cortex. We have previously shown that inhibition of GABA synthesis in the PeF produces panic-vulnerable rats. Here, we investigate the mechanisms by which a panic-vulnerable state could lead to persistent fear. We first show that optogenetic activation of glutamatergic terminals from the PeF to the basolateral amygdala (BLA) enhanced the acquisition, delayed the extinction and induced the persistence of fear responses 3 weeks later, confirming a functional PeF-amygdala pathway involved in fear learning. Similar to optogenetic activation of PeF, panic-prone rats also exhibited delayed extinction. Next, we demonstrate that panic-prone rats had altered inhibitory and enhanced excitatory synaptic transmission of the principal neurons, and reduced protein levels of metabotropic glutamate type 2 receptor (mGluR2) in the BLA. Application of an mGluR2-positive allosteric modulator (PAM) reduced glutamate neurotransmission in the BLA slices from panic-prone rats. Treating panic-prone rats with mGluR2 PAM blocked sodium lactate (NaLac)-induced panic responses and normalized fear extinction deficits. Finally, in a subset of patients with comorbid PD, treatment with mGluR2 PAM resulted in complete remission of panic symptoms. These data demonstrate that a panic-prone state leads to specific reduction in mGluR2 function within the amygdala network and facilitates fear, and mGluR2 PAMs could be a targeted treatment for panic symptoms in PD and PTSD patients.

Insights in the Cardioprotective Mechanism of the New Drug R56865

The compound R56865, a benzothiazolamine derivative, is the prototype of a new class of substances that protect the heart in conditions of [Ca overload. The substance improves postischemic functional recovery and significantly reduces the infarct size in dogs subjected to coronary artery occlusion [for review, (see 1)]. The drug is especially active against arrhythmias and mechanical deterioration induced by cardiac glycoside intoxication (2,3) and postischemic reperfusion (4). In both conditions Na+ /Ca2+ exchange is assumed to be involved in the rise of [Ca2+]i, most likely by a primary increase in [Na]i.

Calcium Overload Blockade in Neurons and Cardiomyocytes

An important role in cell death following an ischemic insult has been attributed to Ca2+, although the mechanisms by which altered Ca2+ homeostasis induces cell injury are poorly understood. A good insight into the factors responsible for abnormal Ca2+ load in brain and heart cells is critical for the development of pharmacological agents that afford protection during ischemia. It is generally assumed that the depletion of ATP during ischemia triggers an impairment of ion homeostasis. Intracellular Ca2+ increases to a concentration which might exceed the equilibrium between influx and extrusion or sequestration capacities. This situation imposes a heavy burden on the already compromised energy household and eventually might be the cause of cell death. In addition to Ca2+. transients, Na+ transients are considered to play a crucial role in the development of ischemic cell damage and Na+ overload might precede excessive Ca2+-influx. Factors liberated during ischemia and reperfusion (e.g., reactive 02 species, lysophosphatides) are known to impair the inactivation kinetics of the Na+ channel causing excessive Na+-entry. The resulting Na+-overload may then drive the Na /Ca2+ -exchanger in the direction of Ca2+-overload. Moreover, altered Na+ channels may directly contribute to Ca2+-overload by carrying Ca2+ in addition to Na+.