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Jason Charng, Zheng He, Algis J Vingrys, Bang V Bui, Rebecca L Fish, Rachel Gurrell, Christine T Nguyen; Anesthesia usage confounds in vivo pharmacological studies using electrophysiology. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6191.
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Anesthesia related confounds during in vivo pharmacological testing are poorly understood. This project employs conscious recordings to quantify the influence of ketamine:xylazine anesthesia on isoguvacine (GABAa agonist) induced changes to the electroretinogram (ERG) and visual evoked responses (VEP).
Long-Evans rats (n=8, male, 3-month old) were implanted with telemetry transmitters to record electrophysiology under conscious conditions. ERG and VEP electrodes on the sclera and above the visual cortex were referenced to a forehead electrode. Isoguvacine was administered via intramuscular (IM 0, 10, 30mg/kg), intracerebroventricular (ICV 6µl, 45mM) or intravitreal (IV 3µl, 180mM) routes and electrophysiology recorded with 5 day washout period in between. Conventional anaesthetized ERG and VEP recordings with chlorided silver electrodes were also recorded in age matched cohort (n=5) following same isoguvacine injections as the conscious group. Responses were measured at 1.52 log cd.s.m-2 and analyzed to return peak amplitudes and timing (mean±SEM).
Under anesthesia, IM isoguvacine produced a significant decrease in a-wave (10mg/kg -10±1%, 30mg/kg -16±2%, p<0.05) and b-wave (10mg/kg -7±1%, 30mg/kg -14±1%, p<0.05) amplitudes compared to vehicle injection. Timing parameters were similar except a significantly slowed a-wave with 30 mg/kg isoguvacine (24.4±0.4 vs 25.5±0.7ms). IM isoguvacine in conscious animals yielded no % difference in a- and b-wave amplitudes compared to vehicle (a-wave: 10mg/kg 33±19%, 30mg/kg 21±14%; b-wave: 10mg/kg 21±9%, 30mg/kg 13±7%) and timings (a-wave: 10mg/kg 6±14%, 30mg/kg -14±7%; b-wave: 10mg/kg 3±4%, 30mg/kg 5±5%). IV isoguvacine in anesthetized animals decreased a-wave (-30±8%, p<0.05), increased b-wave amplitudes (15±5%, p<0.05) and produced faster a-wave (-50±3%, p<0.05) and b-waves (-22±3%, p<0.05). In contrast, IV isoguvacine in conscious animals did not affect ERG amplitude (a-wave 21±20%, b-wave -13±11%) or timing (a-wave -25±11%, b-wave -11±5%). ICV isoguvacine in anesthetized rats reduced P2-N1 amplitude (-52±4%, p<0.05). In conscious rats ICV isoguvacine slowed P2 (26±10%) and N1 (14±4%) peak time but did not affect amplitudes.
We show that ketamine:xylazine anesthesia confounds in vivo electrophysiology. The ability to conduct pharmacology studies without anaesthesia may provide superior clinical translation than conventional techniques.
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