Fear Extinction-Based Inter-Individual and Sex Differences in Pain-Related Vocalizations and Anxiety-like Behaviors but Not Nocifensive Reflexes

Abstract

Inter-individual and sex differences in pain responses are recognized but their mechanisms are not well understood. This study was intended to provide the behavioral framework for analyses of pain mechanisms using fear extinction learning as a predictor of phenotypic and sex differences in sensory (mechanical withdrawal thresholds) and emotional-affective aspects (open field tests for anxiety-like behaviors and audible and ultrasonic components of vocalizations) of acute and chronic pain. In acute arthritis and chronic neuropathic pain models, greater increases in vocalizations were found in females than males and in females with poor fear extinction abilities than females with strong fear extinction, particularly in the neuropathic pain model. Female rats showed higher anxiety-like behavior than males under baseline conditions but no inter-individual or sex differences were seen in the pain models. No inter-individual and sex differences in mechanosensitivity were observed. The data suggest that vocalizations are uniquely suited to detect inter-individual and sex differences in pain models, particularly in chronic neuropathic pain, whereas no such differences were found for mechanosensitivity, and baseline differences in anxiety-like behaviors disappeared in the pain models.

Kappa Opioid Receptor Blockade in the Amygdala Mitigates Pain Like-Behaviors by Inhibiting Corticotropin Releasing Factor Neurons in a Rat Model of Functional Pain

“…Vocalizations in the audible (20 Hz-16 kHz) and ultrasonic (25 ± 4 kHz) ranges were recorded using a microphone and a bat detector, respectively, as in our previous studies ( Han et al, 2005 ; Kiritoshi et al, 2016 ; Mazzitelli and Neugebauer, 2019 ; Presto et al, 2021 ; Mazzitelli et al, 2022 ). Under brief anesthesia with isoflurane, rats were placed in a custom-designed plexiglass chamber that permitted access to the paws for mechanical stimulation (U.S. Patent 7,213,538).…”

Sex Differences in CGRP Regulation and Function in the Amygdala in a Rat Model of Neuropathic Pain

“…For that, rats were briefly anesthetized with isoflurane (2%–3%; precision vaporizer, Harvard Apparatus) and placed slightly restrained in a customized holding chamber that allowed hindlimb access (U.S. Patent 7,213,538). Hindlimb withdrawal thresholds were measured after 30 min of habituation to the holding chamber by using a calibrated forceps with a force transducer (see Section “Emotional-Affective Responses”) to compress the left hindpaw with gradually increasing intensity until a reflex response was evoked, as described in our previous studies (Hein et al, 2021 ; Presto et al, 2021 ). The withdrawal threshold, defined as the force required to evoke a reflex response, was calculated using the average value from three trials.…”

“…Emotional-affective responses were assessed by measuring vocalizations in the ultrasonic (25 ± 4 kHz) range, as described in our previous studies (Ji et al, 2018 ; Mazzitelli and Neugebauer, 2019 ; Hein et al, 2021 ; Mazzitelli et al, 2021 ; Presto et al, 2021 ). Rats were briefly anesthetized with isoflurane (2%–3%; precision vaporizer, Harvard Apparatus) and placed in the custom-designed recording chamber for stable recordings of vocalizations evoked by noxious stimulation.…”

“…The open field test (OFT) was used to measure exploratory behavior in the peripheral and central zones of an open arena (70 cm × 70 cm) with acrylic walls (height, 45 cm). Rat movements were recorded for 15 min using a computerized video tracking and analysis system (EthoVision XT 11 software, Noldus Information Technology) as described previously (Ji et al, 2018 ; Hein et al, 2021 ; Presto et al, 2021 ). Time spent in the center of the arena was calculated during the first 5 min of each experimental trial.…”

Gingerol-Enriched Ginger Supplementation Mitigates Neuropathic Pain via Mitigating Intestinal Permeability and Neuroinflammation: Gut-Brain Connection

“…Lumbar spinal nerve (L5) ligation in this model results in acute hypersensitivity within 1 week that persists for multiple weeks (Chung et al, 2004). The SNL model is well-established in our laboratories (Ji et al, 2017;Ji et al, 2018;Ji and Neugebauer, 2019;Navratilova et al, 2019;Presto et al, 2021;Shen et al, 2022b). In brief, rats were anesthetized with isoflurane (2%-3%; precision vaporizer, Harvard Apparatus) and the left L5 spinal nerve was surgically exposed and tightly ligated using 6-0 sterile silk.…”