Methods On removal from anesthesia with 3% halothane, 10 rats were given a
subcutaneous injection of formalin (5%, 50 μL) into the dorsum of the hindpaw. Behavioral …

The formalin test was introduced as a model of tonic pain in 1977, and has since been used
extensively in rats and mice. In rats, formalin generates an initial phase of activity (5–10 min …

Several studies have demonstrated that the nonselective opioid receptor antagonist
naloxone produces a paradoxical antinociception in the formalin test. The opioid system is …

Formalin injected subcutaneously into the paw is a frequently used pain assay; it evokes an
initial period of licking and flinching followed by a period of quiescence and last by a second …

In contrast to an expected preventive analgesic effect, clinical observations suggest that
intraoperatively applied opioids can induce postoperative hyperalgesia. We tested the …

Considerable debate persists concerning peripheral vs. central mechanisms underlying the
second phase of the nociceptive response in the formalin test in the rat. To gain insight into …

Intraplantar injection of formalin produces persistent spontaneous nociception and
hyperalgesia. The underlying mechanism, however, remains unclear. The present study …

Subcutaneous formalin injection has been used extensively to evaluate acute effects (over
several hours) of chemical nociceptive stimulation on nociceptive reflexes. Also, a persistent …

Objectives: There is controversy about combining opioids with different receptor affinities.
We assessed the analgesic and antihyperalgesic effects of the μ-agonist fentanyl and the …

The present study has assessed the relationship between formalin-induced nociception and
formalin-induced inflammation by comparing the dose-related effects of anti-inflammatory …