Magnus Ivarsson

A Comparison of the α2/3/5 Selective Positive Allosteric Modulators L-838,417 and TPA023 in Preclinical Models of Inflammatory and Neuropathic Pain

GABAA receptors containing α2/3 subunits are current targets in the battle to develop new pain medications, as they are expressed in the spinal cord where increasing inhibitory drive should result in analgesia. However, this approach is prone to a range of side effects including sedation, cognitive impairment, and abuse as a consequence of the widespread influence of GABA. The ability to make subtype selective low-efficacy benzodiazepine compounds, which potentiate the action of GABA at specific α subunits, has the potential to reduce this side effect profile. In this study, we have investigated the effects of the medium-efficacy positive allosteric modulator (PAM) L-838,417 and the low-efficacy PAM TPA023 in a number of preclinical inflammatory and neuropathic pain models. We conclude that either the higher level of efficacy at α2/3 or efficacy at α5 is required for compounds to have a significant analgesic effect in a range of models, and, therefore, although the side-effect profile of compounds can be reduced compared to typical benzodiazepines, it is unlikely that it can be completely eliminated.

A Rodent Model of Traumatic Stress Induces Lasting Sleep and Quantitative Electroencephalographic Disturbances

Hyperarousal and sleep disturbances are common, debilitating symptoms of post-traumatic stress disorder (PTSD). PTSD patients also exhibit abnormalities in quantitative electroencephalography (qEEG) power spectra during wake as well as rapid eye movement (REM) and non-REM (NREM) sleep. Selective serotonin reuptake inhibitors (SSRIs), the first-line pharmacological treatment for PTSD, provide modest remediation of the hyperarousal symptoms in PTSD patients, but have little to no effect on the sleep-wake architecture deficits. Development of novel therapeutics for these sleep-wake architecture deficits is limited by a lack of relevant animal models. Thus, the present study investigated whether single prolonged stress (SPS), a rodent model of traumatic stress, induces PTSD-like sleep-wake and qEEG spectral power abnormalities that correlate with changes in central serotonin (5-HT) and neuropeptide Y (NPY) signaling in rats. Rats were implanted with telemetric recording devices to continuously measure EEG before and after SPS treatment. A second cohort of rats was used to measure SPS-induced changes in plasma corticosterone, 5-HT utilization, and NPY expression in brain regions that comprise the neural fear circuitry. SPS caused sustained dysregulation of NREM and REM sleep, accompanied by state-dependent alterations in qEEG power spectra indicative of cortical hyperarousal. These changes corresponded with acute induction of the corticosterone receptor co-chaperone FK506-binding protein 51 and delayed reductions in 5-HT utilization and NPY expression in the amygdala. SPS represents a preclinical model of PTSD-related sleep-wake and qEEG disturbances with underlying alterations in neurotransmitter systems known to modulate both sleep-wake architecture and the neural fear circuitry.

Retinal biomarkers provide “insight” into cortical pharmacology and disease

&NA; The retina is an easily accessible out‐pouching of the central nervous system (CNS) and thus lends itself to being a biomarker of the brain. More specifically, the presence of neuronal, vascular and blood‐neural barrier parallels in the eye and brain coupled with fast and inexpensive methods to quantify retinal changes make ocular biomarkers an attractive option. This includes its utility as a biomarker for a number of cerebrovascular diseases as well as a drug pharmacology and safety biomarker for the CNS. It is a rapidly emerging field, with some areas well established, such as stroke risk and multiple sclerosis, whereas others are still in development (Alzheimers, Parkinsons, psychological disease and cortical diabetic dysfunction). The current applications and future potential of retinal biomarkers, including potential ways to improve their sensitivity and specificity are discussed. This review summarises the existing literature and provides a perspective on the strength of current retinal biomarkers and their future potential.

State-dependent alterations in sleep/wake architecture elicited by the M4 PAM VU0467154 - Relation to antipsychotic-like drug effects.

Accumulating evidence indicates direct relationships between sleep abnormalities and the severity and prevalence of other symptom clusters in schizophrenia. Assessment of potential state-dependent alterations in sleep architecture and arousal relative to antipsychotic-like activity is critical for the development of novel antipsychotic drugs (APDs). Recently, we reported that VU0467154, a selective positive allosteric modulator (PAM) of the M4 muscarinic acetylcholine receptor (mAChR), exhibits robust APD-like and cognitive enhancing activity in rodents. However, the state-dependent effects of VU0467154 on sleep architecture and arousal have not been examined. Using polysomnography and quantitative electroencephalographic recordings from subcranial electrodes in rats, we evaluated the effects of VU0467154, in comparison with the atypical APD clozapine and the M1/M4-preferring mAChR agonist xanomeline. VU0467154 induced state-dependent alterations in sleep architecture and arousal including delayed Rapid Eye Movement (REM) sleep onset, increased cumulative duration of total and Non-Rapid Eye Movement (NREM) sleep, and increased arousal during waking periods. Clozapine decreased arousal during wake, increased cumulative NREM, and decreased REM sleep. In contrast, xanomeline increased time awake and arousal during wake, but reduced slow wave activity during NREM sleep. Additionally, in combination with the N-methyl-d-aspartate subtype of glutamate receptor (NMDAR) antagonist MK-801, modeling NMDAR hypofunction thought to underlie many symptoms in schizophrenia, both VU0467154 and clozapine attenuated MK-801-induced elevations in high frequency gamma power consistent with an APD-like mechanism of action. These findings suggest that selective M4 PAMs may represent a novel mechanism for treating multiple symptoms of schizophrenia, including disruptions in sleep architecture without a sedative profile.

Evidence of a pharmacodynamic EEG profile in rats following clonidine administration using a nonlinear analysis

Background Changes caused by clonidine in rodent electroencephalograms (EEG) have been reported with some inconsistency. For this reason, a pre-clinical study was conducted in order to confirm previous findings with both a standard spectral analysis and a sleep stage scoring procedure. In addition, a nonlinear technique for analysing the time-varying signals was implemented to compare its performance against conventional approaches. Results The nonlinear method succeeds in quantifying all dose-related responses from the data set relying solely on the EEG trace. Conclusions Nonlinear approaches can deliver a suitable alternative to the sleep-stage scoring methods commonly used for drug effect detection.

In vitro and in vivo pharmacological characterisation of the potent and selective vasopressin V1A receptor antagonist 4-[4-(4-Chloro-phenyl)-5-[1,2,3]triazol-2-ylmethyl-4H-[1,2,4]triazol-3-yl]-piperidin-1-yl-(3,5-difluoro-phenyl) methanone (PF-00738245)

The dysregulation of arginine vasopressin (AVP) release and activation of vasopressin receptors plays an important role in disease conditions including polycystic kidney disease, congestive heart failure and dysmenorrhoea. The development of potent and selective vasopressin receptor ligands is needed to help dissect the function of the specific subtypes in disease pathogenesis. Here we report the pharmacological characterisation of PF-00738245 in in vitro binding and functional assays using cells expressing vasopressin V(₁A), V(₁B) or V₂ receptors. PF-00738245 inhibited AVP binding to the recombinant human vasopressin V(₁A) receptor (K(i)=2.85 nM) and blocked AVP-induced rat aortic ring and human myometrial contraction (pK(B)=7.35 and 8.62 respectively). PF-00738245 was selective for the vasopressin V(1A) receptor by demonstrating minimal binding to vasopressin V(₁B) (3.6% inhibition at 10 μM) or functional activity at vasopressin V₂ receptors (8.1% agonist and -8.4% antagonist activity at 10 μM) as well as the oxytocin receptor (46.3% antagonist activity at 10 μM). The in vivo pharmacological properties were tested orally in the rat and PF-00738245 dose dependently blocked the effect of AVP on a capsaicin-induced cutaneous flare response. Taken together the data support the use of PF-00738245 as a potent and selective vasopressin V(₁A) receptor antagonist which may have utility in the treatment of disease conditions which are propagated by elevation in vasopressin V(₁A) receptor signalling.

Implantation and Recording of Wireless Electroretinogram and Visual Evoked Potential in Conscious Rats

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both laboratory and clinical settings. Currently, preclinical ERG and VEP measurements are performed with anesthesia to ensure stable electrode placements. However, the very presence of anesthesia has been shown to contaminate normal physiological responses. To overcome these anesthesia confounds, we develop a novel platform to assay ERG and VEP in conscious rats. Electrodes are surgically implanted sub-conjunctivally on the eye to assay the ERG and epidurally over the visual cortex to measure the VEP. A range of amplitude and sensitivity/timing parameters are assayed for both the ERG and VEP at increasing luminous energies. The ERG and VEP signals are shown to be stable and repeatable for at least 4 weeks post surgical implantation. This ability to record ERG and VEP signals without anesthesia confounds in the preclinical setting should provide superior translation to clinical data.