The kappa opioid receptor (KOR) and the endogenous peptide-ligand dynorphin have received significant attention due the involvement in mediating a variety of behavioral and neurophysiological responses, including opposing the rewarding properties of drugs of abuse including opioids. Accumulating evidence indicates this system is involved in regulating states of motivation and emotion. Acute act...

Corticotropin-releasing factor (CRF) is an important regulator of physiological functions and behavior in stress. Analgesia is one of the characteristics of stress reaction and CRF is involved in providing stress-induced analgesia, however, the underlying mechanisms remain to be determined. Exogenous CRF mimics stress effects on pain sensitivity and causes analgesic effect. The present study wa...

Two experiments were made showing that opioid involvement coincides with the magnitude of stress-induced analgesia. In Experiment I rats subjected to cold water swims were screened for jump threshold levels on electrified grid and divided into high, medium and low threshold responders' groups. Later on the three groups were given 90 s forepaw footshock. Tail-flick latencies rose highest in the ...

       In this study, we investigated the interactive effects of intraperitoneal (i.p.) injections of three different phosphodiesterase inhibitors (PDEIs) on morphine-induced analgesia in mice using tail-flick method. Subcutaneous administration of morphine (1, 3 and 6 mg/kg) caused significant antinociceptive effects in a dose dependent manner. Administration of pentoxifylline (12.5, 25, 50 an...

This article reviews situations in which stimuli produce an increase or a decrease in nociceptive responses through basic associative processes and provides an associative account of such changes. Specifically, the literature suggests that cues associated with stress can produce conditioned analgesia or conditioned hyperalgesia, depending on the properties of the conditioned stimulus (e.g., con...