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Background: Osteosarcoma (OS) represents the most common primary bone tumor in humans and in companion dogs, being practically phenotypically identical. There is a need for effective treatments to extend the survival of patients with OS. Here, we examine the dosimetry in beagle dogs and cross-reactivity with human tissues of a novel human antibody, IF3, that targets the insulin growth factor receptor type 2 (IGF2R), which is overexpressed on OS cells, making it a candidate for radioimmunotherapy of OS. Methods: [89Zr]Zr-DFO-IF3 was injected into three healthy beagle dogs. PET/CT was conducted at 4, 24, 48, and 72 h. RAPID analysis was used to determine the dosimetry of [177Lu]Lu-CHXA"-IF3 for a clinical trial in companion dogs with OS. IF3 antibody was biotinylated, and a multitude of human tissues were assessed with immunohistochemistry. Results: PET/CT revealed that only the liver, bone marrow, and adrenal glands had high uptake. Clearance was initially through renal and hepatobiliary excretion in the first 72 h followed by primarily physical decay. RAPID analysis showed bone marrow to be the dose-limiting organ with a therapeutic range for 177Lu calculated to be 0.487–0.583 GBq. Immunohistochemistry demonstrated the absence of IGF2R expression on the surface of healthy human cells, thus suggesting that radioimmunotherapy with [177Lu]Lu-CHXA"-IF3 will be well tolerated. Conclusions: Image-based dosimetry has defined a safe therapeutic range for canine clinical trials, while immunohistochemistry has suggested that the antibody will not cross-react with healthy human tissues. [ABSTRACT FROM AUTHOR]

There is significant interest in the use of cannabinoids for the treatment of many epilepsies including absence epilepsy (AE). Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model many aspects of AE including the presence of spike‐and‐wave discharges (SWDs) on electroencephalogram (EEG) and behavioral comorbidities, such as elevated anxiety. However, the effects of cannabis plant‐based phytocannabinoids have not been tested in GAERS. Therefore, we investigated how SWDs in GAERS are altered by the two most common phytocannabinoids, Δ9‐tetrahydrocannabinol (THC) and cannabidiol (CBD), and exposure to smoke from two different chemovars of cannabis. Animals were implanted with bipolar electrodes in the somatosensory cortex and EEGs were recorded for 2 hr. Injected THC (1–10 mg/kg, i.p.) dose‐dependently increased SWDs to over 200% of baseline. In contrast, CBD (30–100 mg/kg, i.p.) produced a ~50% reduction in SWDs. Exposure to smoke from a commercially available chemovar of high‐THC cannabis (Mohawk, Aphria Inc.) increased SWDs whereas a low‐THC/high‐CBD chemovar of cannabis (Treasure Island, Aphria Inc.) did not significantly affect SWDs in GAERS. Pre‐treatment with a CB1R antagonist (SR141716A) did not prevent the high‐THC cannabis smoke from increasing SWDs, suggesting that the THC‐mediated increase may not be CB1R‐dependent. Plasma concentrations of THC and CBD were similar to previously reported values following injection and smoke exposure. Compared to injected CBD, it appears Treasure Island did not increase plasma levels sufficiently to observe an anti‐epileptic effect. Together these experiments provide initial evidence that acute phytocannabinoid administration exerts the biphasic modulation of SWDs and may differentially impact patients with AE. [ABSTRACT FROM AUTHOR]

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are a rodent model of childhood absence epilepsy (CAE) that display a gain‐of‐function mutation in the gene encoding the Cav3.2 T‐type calcium channel. GAERS demonstrate heightened learning and delayed extinction of fear conditioning. Our objective in the present study was to examine the effects of the pan‐T‐type calcium channel blocker Z944 on the acquisition, consolidation and extinction of conditioned fear in GAERS and the non‐epileptic control (NEC) strain. Z944 (10 mg/kg; ip) was administered 15 min prior to either acquisition, extinction day 1 (24 hr later), acquisition and extinction day 1, or during the consolidation (post‐acquisition) of tone‐cued fear conditioning. Extinction was examined 24 and 48 hr after conditioning. In drug naïve GAERS, increased freezing during the acquisition and extinction phases of fear conditioning was found. Short‐term effects of Z944 on performance were observed as Z944 increased freezing during testing on the day it was administered. Z944 administered prior to the acquisition phase had a long‐term effect on extinction. Specifically, both GAERS and NECs showed a decrease in freezing during extinction relative to drug naïve GAERS and NEC rats respectively. Regardless of strain or treatment, female rats showed reduced extinction of fear relative to male rats. These results demonstrate that T‐type calcium channels contribute to the neural systems that mediate the learning and memory of conditioned fear. Overall, these findings suggest that T‐type calcium channel blockers show promise in the treatment of learning impairments observed in disorders such as CAE. [ABSTRACT FROM AUTHOR]

Sudden unexpected death in epilepsy (SUDEP) is a fatal complication of epilepsy in which brainstem spreading depolarization may play a pivotal role, as suggested by animal studies. However, patiotemporal details of spreading depolarization occurring in relation to fatal seizures have not been investigated. In addition, little is known about behavioural and neurophysiological features that may discriminate spontaneous fatal from non-fatal seizures. Transgenic mice carrying the missense mutation S218L in the α1A subunit of Cav2.1 (P/Q-type) Ca2+ channels exhibit enhanced excitatory neurotransmission and increased susceptibility to spreading depolarization. Homozygous Cacna1aS218L mice show spontaneous non-fatal and fatal seizures, occurring throughout life, resulting in reduced life expectancy. To identify characteristics of fatal and non-fatal spontaneous seizures, we compared behavioural and electrophysiological seizure dynamics in freely-behaving homozygous Cacna1aS218L mice. To gain insight on the role of brainstem spreading depolarization in SUDEP, we studied the spatiotemporal distribution of spreading depolarization in the context of seizure-related death. Spontaneous and electrically-induced seizures were investigated by video monitoring and electrophysiological recordings in freely-behaving Cacna1aS218L and wild-type mice. Homozygous Cacna1aS218L mice showed multiple spontaneous tonic-clonic seizures and died from SUDEP in adulthood. Death was preceded by a tonic-clonic seizure terminating with hindlimb clonus, with suppression of cortical neuronal activity during and after the seizure. Induced seizures in freely-behaving homozygous Cacna1aS218L mice were followed by multiple spreading depolarizations and death. In wild-type or heterozygous Cacna1aS218L mice, induced seizures and spreading depolarization were never followed by death. To identify temporal and regional features of seizure-induced spreading depolarization related to fatal outcome, diffusion-weighted MRI was performed in anaesthetized homozygous Cacna1aS218L and wild-type mice. In homozygous Cacna1aS218L mice, appearance of seizure-related spreading depolarization in the brainstem correlated with respiratory arrest that was followed by cardiac arrest and death. Recordings in freely-behaving homozygous Cacna1aS218L mice confirmed brainstem spreading depolarization during spontaneous fatal seizures. These data underscore the value of the homozygous Cacna1aS218L mouse model for identifying discriminative features of fatal compared to non-fatal seizures, and support a key role for cortical neuronal suppression and brainstem spreading depolarization in SUDEP pathophysiology. [ABSTRACT FROM AUTHOR]

Summary: Objective: Genetic alterations have been identified in the CACNA1H gene, encoding the CaV3.2 T‐type calcium channel in patients with absence epilepsy, yet the precise mechanisms relating to seizure propagation and spike‐wave‐discharge (SWD) pacemaking remain unknown. Neurons of the thalamic reticular nucleus (TRN) express high levels of CaV3.2 calcium channels, and we investigated whether a gain‐of‐function mutation in the Cacna1h gene in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) contributes to seizure propagation and pacemaking in the TRN. Methods: Pathophysiological contributions of CaV3.2 calcium channels to burst firing and absence seizures were assessed in vitro using acute brain slice electrophysiology and quantitative real‐time polymerase chain reaction (PCR) and in vivo using free‐moving electrocorticography recordings. Results: TRN neurons from GAERS display sustained oscillatory burst‐firing that is both age‐ and frequency‐dependent, occurring only in the frequencies overlapping with GAERS SWDs and correlating with the expression of a CaV3.2 mutation‐sensitive splice variant. In vivo knock‐down of CaV3.2 using direct thalamic injection of lipid nanoparticles containing CaV3.2 dicer small interfering (Dsi) RNA normalized TRN burst‐firing, and in free‐moving GAERS significantly shortened seizures. Significance: This supports a role for TRN CaV3.2 T‐type channels in propagating thalamocortical network seizures and setting the pacemaking frequency of SWDs. [ABSTRACT FROM AUTHOR]

Carbamazepine (CBZ) is a first-line antiepileptic agent with mood-stabilizing effects in bipolar disorder. It has been reported to influence extracellular concentrations of serotonin and dopamine, suggesting an interaction with monoamine transporters. We have investigated this effect using in vivo single photon emission computed tomography (SPECT) in rats. Adult male rats received 3 mg/kg/h CBZ via mini-osmotic pump. After 14 days continuous treatment, animals underwent two consecutive SPECT scans, using 125I β-CIT as a radiotracer to label serotonin transporter (SERT) and dopamine transporter (DAT) sites in the brain. Pharmacologic distinction was enabled by 125I β-CIT SPECT imaging in rats acutely exposed to the serotonin and dopamine transporter inhibitors, fluoxetine and GBR12909. The interaction between CBZ and 125I β-CIT binding to SERT and DAT was investigated using in vitro autoradiography. Carbamazepine (10 μm) did not affect binding of 125I β-CIT to isolated rat brain slices, thereby excluding a direct effect on ligand binding to SERT and DAT. SPECT studies with fluoxetine and GBR12909 highlighted SERT binding in thalamus, hippocampus, centromedial nuclei, and occipital cortex, and DAT binding in the caudate. Prolonged treatment with CBZ failed to influence 125I β-CIT binding to either SERT or DAT in any of the brain regions examined. This study employed the novel technique of small animal SPECT imaging to investigate the effects of CBZ on monoamine transporters in rat brain. Following prolonged treatment, the drug was without effect on SERT or DAT availability. The mechanism by which CBZ exerts its mood stabilizing effects remains elusive. [ABSTRACT FROM AUTHOR]

Low-voltage-activated, or T-type, calcium (Ca2+) channels are believed to play an essential role in the generation of absence seizures in the idiopathic generalized epilepsies (IGEs). We describe a homozygous, missense, single nucleotide (G to C) mutation in the Cav3.2 T-type Ca2+ channel gene (Cacna1h) in the genetic absence epilepsy rats from Strasbourg (GAERS) model of IGE. The GAERS Cav3.2 mutation ( gcm) produces an arginine to proline (R1584P) substitution in exon 24 of Cacna1h, encoding a portion of the III-IV linker region in Cav3.2. gcm segregates codominantly with the number of seizures and time in seizure activity in progeny of an F1 intercross. We have further identified two major thalamic Cacna1h splice variants, either with or without exon 25. gcm introduced into the splice variants acts "epistatically," requiring the presence of exon 25 to produce significantly faster recovery from channel inactivation and greater charge transference during high-frequency bursts. This gain-of-function mutation, the first reported in the GAERS polygenic animal model, has a novel mechanism of action, being dependent on exonic splicing for its functional consequences to be expressed. [ABSTRACT FROM AUTHOR]

Abstract: Two-pore domain potassium (K2P) channels are proposed to underlie the background or leak current found in many excitable cells. Extensive studies have been performed investigating the inhibition of K2P2.1 by Gαq- and Gαs-coupled G-protein-coupled receptors (GPCRs), whereas in the present study we investigate the mechanisms underlying Gαi/Gαo-coupled GPCR increases in K2P2.1 activity. Activation of mGlu4 increases K2P2.1 activity, with pharmacological inhibition of protein kinases and phosphatases revealing the involvement of PKA whereas PKC, PKG or protein phosphatases play no role. Mutational analysis of potential C-terminal phosphorylation sites indicates S333 to control approximately 70%, with S300 controlling approximately 30% of the increase in K2P2.1 activity following mGlu4 activation. These data reveal that activation of mGlu4 leads to an increase in K2P2.1 activity through a reduction in C-terminal phosphorylation, which represents a novel mechanism by which group III mGlu receptors may regulate cell excitability and synaptic activity. [Copyright &y& Elsevier]