An ethological evaluation of hot plate response patterns in rats pre- and post-endometriosis induction surgery

(1) Background: Endometriosis, a chronic gynecological disorder, is linked to increased pain sensitivity. The hot-plate test quantifies acute thermal pain in animal models, with plate temperatures typically between 48–56°C but also ranging from 44°C to 80°C. During hot-plate testing in rats, behaviors are categorized into exploration, grooming, pain-related, and escape responses; these can be quantified by latency and frequency. However, the lack of standardized hot-plate temperatures in endometriosis models complicates the interpretation of behavioral thresholds. This study assessed whether hot plate temperatures at 42°C versus 52°C affect thresholds for nociceptive and non-nociceptive behaviors before and after endometriosis surgery; (2) Methods: Female Sprague–Dawley rats (n=8/group) were exposed to 42°C or 52°C hot plates. Endometriosis was induced by attaching four 2x2 mm uterine horn segments to the intestinal mesentery on day 0. Pain-related behaviors were assessed before surgery and one week after; (3) Results: After surgery, animals at 42°C froze faster and more often, showing altered pain response but not increased pain. Behavioral analysis showed temperature-dependent effects: surgery led to quicker and more frequent exploration without lowering pain or escape thresholds. At 52°C, post-surgery rats jumped more frequently, leaned sooner and more often, and exhibited faster and more frequent pain-related behaviors (forepaw- and hindpaw-licking). The frequency of forepaw-licking decreased after surgery. Surgery significantly reduced latency and increased frequency of pain behaviors, with no change in escape or grooming. (4) Conclusions: These findings suggest increased distress and changed pain sensitivity at 42°C, and clear post-surgical hyperalgesia at 52°C.