Acute stress regulates nociception and inflammatory response induced by bee venom in rats: possible mechanisms

Chronic restraint stress exacerbates nociception and inflammatory response induced by bee venom in rats: the role of the P2X7 receptors

OBJECTIVE

Chronic restraint stress exacerbates pain and inflammation. The present study was designed to evaluate the effect of chronic restraint stress on inflammatory pain induced by subcutaneous injection of bee venom (BV).

METHODS

First, we investigated: (1) the effect of two-week restraint stress with daily 2 or 8 h on the baseline paw withdrawal mechanical threshold (PWMT), paw withdrawal thermal latency (PWTL) and paw circumference (PC); (2) the effect of chronic stress on the spontaneous paw-flinching reflex (SPFR), decrease in PWM, PWTL and increase in PC of the injected paw induced by BV.

RESULTS

The results showed that (1) chronic restraint decreased significantly the PWMT and inhibited significantly the increase in PC, but had no effect on PWTL, compared with control group; (2) chronic restraint enhanced significantly BV-induced SPFR and inflammatory swelling of the injected paw. In a second series of experiments, the role of P2X7 receptor (P2X7R) in the enhancement of BV-induced inflammatory pain produced by chronic restraint stress was determined. Systemic pretreatment with P2X7R antagonist completely reversed the decrease in PWMT produced by chronic restraint, inhibited significantly the enhancement of BV-induced inflammatory pain produced by chronic restraint stress.

CONCLUSION

Taken together, our data indicate that chronic restraint stress-enhanced nociception and inflammation in the BV pain model, possibly involving the P2X7R.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Cannabidiol and endogenous opioid peptide-mediated mechanisms modulate antinociception induced by transcutaneous electrostimulation of the peripheral nervous system

Transcutaneous electrical nerve stimulation (TENS) is a non-pharmacological therapy for the treatment of pain. The present work investigated the effect of cannabidiol, naloxone and diazepam in combination with 10 Hz and 150 Hz TENS. Male Wistar rats were submitted to the tail-flick test (baseline), and each rodent received an acute administration (intraperitoneal) of naloxone (3.0mg/kg), diazepam (1.5mg/kg) or cannabidiol (0.75 mg/kg, 1.5mg/kg, 3.0mg/kg, 4.5mg/kg, 6.0mg/kg and 12.0mg/kg); 10 min after the acute administration, 10 Hz or 150 Hz TENS or a sham procedure was performed for 30 min. Subsequently, tail-flick measures were recorded over a 90-min period, at 5-min intervals. 10 Hz TENS increased the nociceptive threshold during the 90-min period. This antinociceptive effect was reversed by naloxone pre-treatment, was not altered by diazepam pre-treatment and was abolished by cannabidiol pre-treatment (1.5mg/kg). Moreover, 150 Hz TENS increased tail-flick latencies by 35 min post-treatment, which was partially inhibited by naloxone pre-treatment and totally inhibited by cannabidiol (1.5mg/kg). These data suggest the involvement of the endogenous opioid system and the cannabinoid-mediated neuromodulation of the antinociception induced by transcutaneous electrostimulation at 10 Hz and 150 Hz TENS.