ABSTRACT
Objective· Formalin is a classic and most widely used algogenic substance,but its itchy effect is not clear.The present study aims to explore the hypothesis that formalin may induce itch as well as pain.Methods· Flinching,as well as licking and forelimb wiping of the site of injection were counted as pain responses,whereas biting and hind paw scratching of the cheek were counted as itchy responses.To discriminate formalin-induced sensations in rats,the irritant (saline as control) was injected,and then pain and itchy responses were recorded.Results · Intraplantar injection of formalin elicited biphasic behavior responses characterized as flinching,as well as biting or licking of the hind paw without significant gender differences.Following intradermal administration of formalin to the cheek,rats exhibited episodic forelimb wiping of the cheek,representative of pain.No gender difference was noticed for this type of behavior.In addition,episodes of hind paw scratches of the cheek,representative of pruritoceptive responses,also occurred.Interestingly,hind paw scratches appeared to be more pronounced in male than in female rats.Conclusion · Intradermal administration of formalin elicits pruritoceptive as well as nociceptive responses in rats.
ABSTRACT
Objective: Formalin is a classic and most widely used algogenic substance, but its itchy effect is not clear. The present study aims to explore the hypothesis that formalin may induce itch as well as pain. Methods: Flinching, as well as licking and forelimb wiping of the site of injection were counted as pain responses, whereas biting and hind paw scratching of the cheek were counted as itchy responses. To discriminate formalin-induced sensations in rats, the irritant (saline as control) was injected, and then pain and itchy responses were recorded. Results: Intraplantar injection of formalin elicited biphasic behavior responses characterized as flinching, as well as biting or licking of the hind paw without significant gender differences. Following intradermal administration of formalin to the cheek, rats exhibited episodic forelimb wiping of the cheek, representative of pain. No gender difference was noticed for this type of behavior. In addition, episodes of hind paw scratches of the cheek, representative of pruritoceptive responses, also occurred. Interestingly, hind paw scratches appeared to be more pronounced in male than in female rats. Conclusion: Intradermal administration of formalin elicits pruritoceptive as well as nociceptive responses in rats.
ABSTRACT
Numerous studies have demonstrated that estrogens may exert multifaceted effects on the cardiovascular system via activating the classical nuclear receptors ERα or ERβ and the novel G protein coupled estrogen receptor (Gper). However, some studies have reported inconsistent cardiovascular phenotypes in Gper-deficient mice. The current study was aimed to reveal the effects of genetic deletion of Gper on the arterial blood pressure (ABP) and heart rate in rats. Gper-deficient Sprague-Dawley rats were generated by utilizing the CRISPR-Cas9 gene-editing technique. ABP of 10-week old male (n = 6) and 12-week old female (n = 6) Gper-deficient rats and age-matched wild type (WT) rats (6 females and 6 males) were measured under awake and restrained conditions through the non-invasive tail-cuff method daily for 8 (females) or 9 days (males). In the male WT rats, ABP and heart rate were slightly higher in day 1 to 4 than those in day 5 to 9, indicative of stress-related sympathoexcitation in the first few days and gradual adaptation to the restrained stress in later days. Gper-deficient rats had significantly higher ABP initially (male: day 1 to day 5; female: day 1 to day 3) and similar ABP in later days of measurement compared with the WT rats. The heart rate of male Gper-deficient rats was consistently higher than that of the male WT rats from day 1 to day 8. Both male and female Gper-deficient rats appeared to show slower body weight gain than the WT counterparts during the study period. Under anesthesia, ABP of Gper-deficient rats was not significantly different from their WT counterparts. These results indicate that Gper-deficient rats may be more sensitive to stress-induced sympathoexcitation and highlight the importance of Gper in the regulation of the cardiovascular function in stressful conditions.