Effects of Formalin-Induced Pain on ACTH, Beta-Endorphin, Corticosterone and Interleukin-6 Plasma Levels in Rats

Abstract

The behavioral and immunoendocrine effects of formalin-induced pain were studied in male rats following a subcutaneous injection of formalin (50 µl; 0.1%, F01 groups, 10%, F10 groups) or sham injection (control groups). After treatment, animals were tested in a transparent open field for either 30 or 60 min and thereafter sacrificed by decapitation. Plasma was collected for adrenocorticotropic hormone (ACTH), corticosterone, β-endorphin (β-EP) and interleukin-6 (IL-6) determinations. Pain-evoked responses (licking, flexing, paw jerk), standard measures of activity (locomotion, rearing, olfactory exploration) and self-grooming were recorded. The higher formalin concentration induced stronger pain-evoked behavioral responses, paralleled by higher levels of ACTH, β-EP and IL-6, but did not affect the other behavioral parameters. In contrast, the lower formalin concentration induced a marked increase in locomotion and rearing and a decrease in ACTH levels. In both formalin-injected groups, corticosterone did not differ from controls.

Persistent Pain Produces Stress-like Alterations in Hippocampal Neurogenesis and Gene Expression

“…63 For quantification of mechanical sensitivity thresholds, von Frey monofilaments (Stoelting, Wood Dale, IL) of graded bending forces (2.6-522 mN) were used as previously described. 6,63 Thermal and mechanical baseline measurements of both hind paws were taken for each animal before pain or stress stimuli and at 2,4,7,9,11,14,18, and 21 (where applicable) days following the treatments to measure hyper-or hypoalgesia. When the animals were killed, hind paws were removed just above the tibiotarsal joint and weighed to measure edema.…”

Exaggerated Response of a Vasopressin–Enhanced Green Fluorescent Protein Transgene to Nociceptive Stimulation in the Rat

“…Nociceptive stimulation elicits a plethora of neuroendocrine responses including arginine vasopressin (AVP) release (Kendler et al, 1978;Onaka et al, 1986Onaka et al, , 1996Onaka and Yagi, 1988) and activation of the hypothalamo-pituitary-adrenal (HPA) axis (Aloisi et al, 1995(Aloisi et al, , 1996Pacák et al, 1995;Culman et al, 1997;Persoons et al, 1997;Taylor et al, 1998). The formalin test for nociception is commonly used in rats and mice to assess the response of an animal to moderate, continuous pain (Abbott et al, 1982a), and this model is thought to resemble clinical pain (Dubuisson and Dennis, 1977;Dennis and Melzack, 1980;Abbott et al, 1982a,b).…”

Unilateral adrenalectomy attenuates hemorrhagic shock-induced analgesia in rats

“…The formalin test is a stressful stimulus. However, it was reported that corticosterone did not increase after formalin injection in normal rats [15]. Another investigator reported that formalin stimulus activated the pituitary-adrenocortical system, but that the resulting release of corticosterone did not affect nociceptive processing [16].…”