Behavioral Assessment of Tramadol and Meloxicam Effects on Postoperative Pain in a Rat Craniotomy Model
Stereotaxic surgery is a common procedure in neuroscience, yet effective analgesic protocols require further study and refinement to optimize the analgesia used in invasive procedures and to improve animal welfare. This study evaluated the effects of tramadol and meloxicam, alone or combined, on pain management following craniotomy in rats. Forty Wistar-Han rats were divided into 5 groups: saline + anesthesia (SAL+ANE), saline + surgery (SAL+SUR), tramadol + surgery (TRA+SUR), meloxicam + surgery (MEL+SUR), and tramadol/meloxicam + surgery (TRA/MEL+SUR). Treatments (saline, 0.2 mL; tramadol, 17.8 mg/kg; meloxicam, 1.5 mg/kg) were administered subcutaneously every 12 h for 72 h. The animals underwent anesthesia or surgery 30 min after the first injection. Postoperative assessments included open field testing, a grooming transfer test, nesting behavior, body weight, and food/water intake. Surgery induced behavioral changes occured within 48 h. SAL+SUR and MEL+SUR groups showed increased locomotion and rearing, while SAL+SUR, TRA+SUR, and TRA/MEL+SUR groups had reduced grooming. TRA/MEL+SUR and SAL+SUR groups had the lowest grooming transfer test scores, and TRA/MEL+SUR rats displayed reduced nesting behavior. Craniotomy caused mild pain lasting at least 48 h. Although no optimal analgesic was identified, providing analgesia and refining surgical techniques are essential to ensure animal welfare.
Nesting behavior scoring. Score 1: Nesting material remains intact and in its original position. Score 2: Nesting material shows minimal handling, with slight evidence of biting (>90% remains intact). Score 3: Approximately 25% to 50% of the nesting material is shredded. Score 4: Between 50% and 90% of the nesting material is shredded but still largely remains in its original position. Score 5: Nesting material is completely shredded and dispersed throughout the cage.
Experimental timeline. The graphical representation of the timeline of shows procedures made during the experiment. The first half of the experiment consists of the preoperative treatment application; 30 min later the surgery occurs, and 90 min after the surgery the OF test is made. The second half of the experiment consists of a 72-h cycle where the GTT, body weight, food and water intake, NB, and treatment administration are repeated. The graphical design was made using the BioRender.
Locomotor and rearing behaviors of rats measured 90 min and 24 h after anesthesia or surgery. (A) Distance traveled (cm), (B) average velocity (cm/s), and (C) movement duration (s) across groups in the OF are shown, as are (D) frequency and (E) duration of rearing behavior (s). *, P < 0.05; **, P < 0.01; ***, P < 0.001.
Grooming behavior and subtypes in rats at 90 min and 24 h after anesthesia or surgery. (A) Frequency and (B) duration (s) of total grooming behaviors are shown. Subtypes of grooming are shown in (C) frequency and (D) duration at 90 min, as well as (E) frequency and (F) duration at 24 h. Grooming subtypes include cephalic (Ceph.), caudal (Caud.), sequential (Seq.), and variations (var.) in grooming or scratching (Scrat.). *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.
Grooming transfer test scores during the first 72 h after surgery. (A) 24 h, (B) 48 h, and (C) 72 h after surgery. Each graph shows pain scores (y-axis) measured at various time points (x-axis) in hours. Treatment groups include SAL+ANE, SAL+SUR, TRA+SUR, MEL+SUR, and TRA/MEL+SUR. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. Error bars represent the SEM.
Body weight gain and water and food/intake evaluation during the first 72 h after surgery. (A) Weight gain (y-axis in grams) measured at 24, 48, and 72 h (x-axis). (B) Water intake (y-axis in mL) measured at the same intervals. (C) Food intake (y-axis in grams) measured at 24, 48, and 72 h. Treatment groups include SAL+ANE, SAL+SUR, TRA+SUR, MEL+SUR, and TRA/MEL+SUR. *, P < 0.05; **, P < 0.01. Error bars represent the SEM.
Nesting behavior scores during the first 72 h after surgery. Shown are the nesting behavior scores (y-axis) for rats across different treatment groups over a 72-h postoperative period. Each graph represents a distinct time point: (A) 24 h, (B) 48 h, and (C) 72 h after surgery. The x-axis indicates time intervals after surgery (4, 6, 8, 10, and 24 h). Treatment groups are SAL+ANE, SAL+SUR, TRA+SUR, MEL+SUR, and TRA/MEL+SUR. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****P < 0.0001. Error bars represent the SEM.
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