No negative effects of intra-abdominal bio-logger implantation under general anaesthesia on spatial cognition learning in a hibernator the edible dormouse

Abstract

The effect of hibernation on cognitive capacities of individuals is not fully understood, as studies provide conflicting results. Most studies focus on behavioural observations without taking the physiological state of individuals to account. To mechanistically understand the effect of hibernation on the brain, physiological parameters need to be included. The implantation of bio-loggers can provide insights on i.e. body temperature without further manipulation of the animals. Surgeries and anaesthesia, however, can harm animals' health and cause cognitive dysfunction, potentially biasing data collected through bio-loggers. We investigated the effects of bio-logger implantation surgery on cognitive performance and learning, controlling for animal and study design characteristics. First, juvenile dormice successfully learned to solve a spatial cognition task using a vertical maze. Distance, transitions, velocity, and duration were measured as indicators for performance. After training, bio-loggers were implanted intra-abdominally under general anaesthesia. Animals were re-tested in the maze two weeks after. We found no effect of bio-logger implantation and surgery on performance. This study is the first to show spatial cognition learning in edible dormice and provides a full description of the peri-anaesthetic management and a protocol for bio-logger implantation surgery in dormice. Importantly, measures were taken to mitigate common anaesthetic complications that could lead to post-operative cognitive dysfunction and influence animal behaviour. By pairing physiological measurements through bio-logger implantation with behaviour and cognition measurements, future research will significantly advance the understanding on mechanisms of learning and behaviour.

Fig 1. Schematic figure of the vertical maze 1 m x 1 m that was used as the spatial cognition task to be solved by juvenile edible dormice n = 51.

The dashed line represents the shortest and direct path (261 cm). Performance was measured as distance, transitions, velocity and duration.

Fig 2. Mean performance in maze over different sessions, n = 51, maximum time limit 30 min per animal.

First Training corresponds to the first training session where animals were unexperienced, maximum 3 Trials. Pre-Surgery corresponds to the last training session 1 day prior to surgery and 13 days after the first trainings session, maximum 7 Trials. Post-surgery corresponds to the first test session after surgery and 14 days of recovery, maximum 5 Trials A) Mean distance in cm covered in maze over trials. Shortest distance to pass through the maze: 261 cm B) Mean transitions (counts) from direct path per trial, minimum transition counted: 1 (i.e. entering the maze-frame) C) mean velocity in cm/s D) mean duration per trial in seconds.

Fig 3. Performance in the maze in different sessions: First time, pre-surgery and post-surgery, n = 51.

First session corresponds to the first training session where animals were unexperienced. Pre-Surgery corresponds to the last training session 1 day prior to surgery and 13 days after the first trainings session. Post-surgery corresponds to the first test session after surgery and 14 days of recovery A) Distance in cm covered in maze, direct path = 261cm B) Transitions from the direct path C) Velocity of animals in cm/s D) Duration in seconds to finish trials. Differences between first vs. pre-surgery session and first vs. post-surgery session were significant for every performance variable. Significant differences at ≤0.01, ≤0.001, ≤0.0001, levels are highlighted using **,*** and **** respectively.

Fig 4

Monitoring of physiological parameters during anaesthesia a) Pulse rate (PR) in beats per minute (Time) b) Respiratory rate (RR) in breaths per minute (Time) c) Oxygen saturation (SpO2) in % over time.