Buprenorphine, but not lidocaine, effectively attenuates post-operative thermal hypersensitivity in an incisional model in neonatal rats (Rattus norvegicus)

Abstract

There is limited information on safe and effective neonatal rodent analgesia. The aim of this study was to evaluate the efficacy and duration of analgesia provided by buprenorphine (Bup) and lidocaine (Lid) in an incisional pain model. Male and female postnatal day three Sprague Dawley rat pups (n=40) were randomly assigned to one of five treatment groups: 1) Saline - 0.1 ml subcutaneous (SC)/0.01 ml saline incisional infiltration; 2) BupL - 0.025 mg/kg Bup, SC/0.01 ml saline infiltration; 3) BupH - 0.05 mg/kg Bup, SC/0.01 ml saline infiltration; 4) LidL - 2 mg/kg lidocaine infiltration/0.1 ml saline SC; and 5) LidH - LDC 4 mg/kg lidocaine infiltration/0.1 ml saline SC. Rat pups were anesthetized with sevoflurane by mask, and a 1-cm full thickness skin incision was made over the left lateral thigh. Infiltration of lidocaine or saline occurred prior to wound closure with surgical glue. Baseline thermal latency was measured 24 hr prior to surgery, and subsequently 1, 2, 4, 8, 24, and 48-hrs post-operatively using an infrared diode laser. Thermal latency in the Saline group was significantly reduced compared to baseline up to the 4 hr timepoint. Both BupL and BupH attenuated thermal hypersensitivity for at least 4 hours in this model. LidL attenuated thermal hypersensitivity for 1 hr and LidH failed to attenuate thermal hypersensitivity. No abnormal clinical signs were noted for all treatment groups throughout the study. In summary, a single pre-operative dose of buprenorphine 0.025 to 0.05 mg/kg (SC) effectively attenuated postoperative thermal hypersensitivity in 3-day old neonatal rat incisional pain model for 4 hours.