V.O. Molodtsov¹, V.Y. Smirnov², S.D. Solnushkin³, V.N. Chikhman4
1,2 St. Petersburg State Electroechnical University “LETI” named after V.I. Ulyanov (Lenin) (St.-Petersburg, Russia)
3,4 Pavlov Institute of Physiology, Russian Academy of Sciences (St.-Petersburg, Russia)
One of the areas of experimental physiological research is the study of pain. One of the common pain stimuli used in many laboratories in the world is electric current. In behavioral experiments, a common way of organizing an electrical impact on a moving laboratory animal is to apply electrical voltage to the metal bars of the experimental cage floor. When the animal locks bars with different potential, it receives an electrical shock. It is desirable during the experiment to change the polarity of the electric potential on the bars of the lattice, in order to minimize the ability of the animal to avoid electrical exposure, located on the bars with the same electric potential. The sequence of polarity reversal on metal bars of the cage floor was organized in such a way that not a single pair of bars had the same polarity during the supply cycles of electric current pulses and the animal received an electrical shock at least once per cycle when it closed any pair of bars.
Experimental techniques are known in which the voltage applied to the cage floor between adjacent conductive bars is manually controlled by means of a transformer with control of the voltage value on the voltmeter. In this case, the determination of the threshold of pain sensitivity occurs with an error due to a large, manually adjustable pitch of change in electrical voltage. In a number of experiments, it is desirable to provide a more accurate setting of the minimum values of the voltage level and the registration of the current value characterizing the minimum pain sensitivity threshold, as well as to ensure accurate repeatability of the steps of voltage level variation in different experiments with different animals. In order to exclude the possibility for animals to find equipotential bars of the cage floor to avoid electrical shock, for example, they apply electric stimulation independently to each conductive bar of the cage floor, providing a multiphase pulse repetition mode. For accurate and effective determination of the pain threshold of laboratory animals, the device MD280 was developed and implemented. Each electronic key in the device is connected to a specific register bit, and each bar of the cage floor is connected via an electronic key to a controlled constant-voltage source. In turn, the register and voltage source are connected to a control unit connected to the computer via a USB controller. In addition, the device provides correct information by eliminating the possibility of an animal avoiding electrical impact by implementing control of the pulse feed sequence with adjustable phasing (set by the time shift of the pulses on the conductive bars of the floor) and by fixing and saving the measurement sequence at each step of changing the parameters. Interaction with the device is carried out using a computer with USB 2.0 Full-Speed. Data exchange with the PC via the USB interface is performed by a USB-FIFO converter implemented on an FT245RL (FTDI) chip and a block that converts data from the FIFO buffer into internal commands and records data into the FIFO buffer from the device. The program RatCage has been developed, which provides, on the basis of the device, a study of the threshold pain sensitivity of rats. The graphical interface of the program allows at the start of work to select the parameters of the experiment: electrostimulating effects (constant, pulsed, phased, etc.), setting the values of the impact parameters (voltage amplitude, pulse duration, frequency), how parameters change (automatically or manually). After the start of the measurement signal is applied, the voltage amplitude gradually increases. The experimenter observes the behavior of the laboratory animal (rat) and when the primary nociceptive reaction (startle) appears, presses the “Remember” button. The program allows you to save these values along with the experiment protocol in the experimental database. This ensures an effective measurement of the minimum pain sensitivity threshold due to the smooth adjustment of the parameters of the electrical effect pattern (amplitude, duration, frequency of impulses, their number), automatic measurement of parameters when an animal’s primary nociceptive reaction occurs, and also the avoidance of the possibility that the animal avoids electrical impact by feeding electrical pulses with phasing. The developed approach and the implemented tools have been used in pain studies conducted at the I.P. Pavlov Institute of Physiology RAS.
Molodtsov V.O., Smirnov V.Y., Solnushkin S.D., Chikhman V.N. Hardware and software of behavior experiments. Biomedicine Radioengineering. 2021. V. 24. № 1. Р. 42−47. DOI: 10.18127/j15604136-202101-06 (In Russian).
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