Evaluation sensorimotor of the female and male Wistar rats after painful stimulation in the neonatal period during the development

Abstract

Evidence suggests that painful procedures performed in neonates in a Neonatal Intensive Care Unit (NICU) may lead to an awareness of their responses to pain in the long time. The exposure of newborn pain may be predictive of global responses to pain in childhood and adulthood. However, there are few investigations about the painful effects on sensorimotor development in the long term, particularly in experimental models. The aim of this study was to evaluate the sensorimotor development of Wistar rats exposed to painful stimulation after birth. For the study will be used 64 animals to be followed from birth to 180 days of life. The animals will be separated into four groups: control females (n = 16), control males (n = 16), female pain (n = 16) and male pain (n = 16). Animals in group pain will undergo painful procedures which consist of rapid needles in regions lateral and plantar hind paw right after birth for 15 consecutive days. The control group will be submitted to tactile stimuli using a cotton swab, and lateral regions of the plantar hind paw, soon after birth for 15 consecutive days. All animals will be evaluated at 15, 30, 60, 90, 120, 150 and 180 days. Functional assessment will consist of motor and sensory evaluation by testing paw withdrawal with the von Frey monofilament (for investigation of mechanical allodynia), paw pressure test (for investigation of mechanical hyperalgesia) and Grip Strength Meter (GSM) (for analysis of grip strength). Animals are weighed, placed in individual acrylic boxes for 15 minutes period of adaptation to the environment, then receive tactile stimuli with von Frey monofilaments, starting with the filament of lesser value, so increasing the response to withdrawal of paw. The mechanical hyperalgesia is assessed by paw pressure test, where a forceps is connected to two "strain gauges" strain gauges connected to a digital indicator. During the test, the investigator has a compression arms of forceps device which is then converted to the hind paw of the animal, the force applied by the examiner is gradually increased, until the animal withdraws its paw, and then, the device records the values obtained. For evaluation of grip strength, the animals will be placed in the GSM, with their hind legs facing the bar, then being encouraged to grab the bar of the device, soon after the examiner has a small force, the animal away from the apparatus, the grip strength is then determined by the strength (average) recorded in GSM. The statistical analysis is performed by comparing the data between males and females (Student's t test for unpaired data with normal distribution) and between different ages in the same genre (One way ANOVA, followed by a post-test Tukey test for data with normal distribution). Differences are considered significant when p <0.05.