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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 ...

Pfizer Neusentis

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

The electroretinogram (ERG, retina) and visual evoked potential (VEP, brain) are widely used in vivo tools assaying the integrity of the visual pathway. Current recordings in preclinical models are conducted under anesthesia, which alters neural physiology and contaminates responses. We describe a conscious wireless ERG and VEP recording platform in rats. Using a novel surgical technique to chronically implant electrodes subconjunctivally on the eye and epidurally over the visual cortex, we are able to record stable and repeatable conscious ERG and VEP signals over at least 1 month. We show that the use of anaesthetics, necessary for conventional ERG and VEP measurements, alters electrophysiology recordings. Conscious visual electrophysiology improves the viability of longitudinal studies by eliminating complications associated with repeated anaesthesia. It will also enable uncontaminated assessment of drug effects, allowing the eye to be used as an effective biomarker of the central nervous system.

Conscious wireless electroretinogram and visual evoked potentials in rats.

We describe a novel approach to analyze fluorescein angiography to investigate fluorescein flow dynamics in the rat posterior retina as well as identify abnormal areas following laser photocoagulation.

Quantitative spatial and temporal analysis of fluorescein angiography dynamics in the eye.

The objective of these clinical studies was to assess the safety and urate lowering activity of a novel urate transporter 1 (URAT1)/ xanthine oxidase (XO) inhibitor PF-06743649 in healthy subjects and gout patients. Escalating doses of PF-06743649 or placebo were given to healthy young subjects, healthy elderly subjects and gout patients. Serum uric acid (sUA) and urinary pharmacodynamic markers were assayed, and safety was assessed by collection of adverse events and assessment of safety labs, ECGs and vital signs. Administration of PF-06743649 led to rapid decrease in sUA in all cohorts; in gout patients, a change from baseline of 69 % was observed for the 40 mg dose. Urinary and serum biomarkers were consistent with inhibition of both URAT1 and XO. Although dosing was otherwise well tolerated, two subjects experienced serious adverse events of acute kidney injury. Both subjects exhibited increased serum creatinine and blood urea nitrogen in the first 3 days post first dose and were hospitalised. One subject exhibited oliguria for the first 24 h. Both subjects made a complete recovery with minimal intervention. PF-06743649 was effective at rapidly lowering sUA, but further development was terminated for an identified renal safety risk.

Acute kidney injury observed during phase 1 clinical trials of a novel xanthine oxidase/URAT1 dual inhibitor PF-06743649.

Objective. To examine whether retinal electrophysiology is a useful surrogate marker of drug penetrance into the central nervous system (CNS). Materials and Methods. Brain and retinal electrophysiology were assessed with full-field visually evoked potentials and electroretinograms in conscious and anaesthetised rats following systemic or local administrations of centrally penetrant (muscimol) or nonpenetrant (isoguvacine) compounds. Results. Local injections into the eye/brain bypassed the blood neural barriers and produced changes in retinal/brain responses for both drugs. In conscious animals, systemic administration of muscimol resulted in retinal and brain biopotential changes, whereas systemic delivery of isoguvacine did not. General anaesthesia confounded these outcomes. Conclusions. Retinal electrophysiology, when recorded in conscious animals, shows promise as a viable biomarker of drug penetration into the CNS. In contrast, when conducted under anaesthetised conditions confounds can be induced in both cortical and retinal electrophysiological recordings.

Rachel Gurrell

Pfizer Neusentis

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