Periodic abstinence enhances nociception without significantly altering the antinociceptive efficacy of spinal morphine in the rat

Withdrawal-associated injury site pain prevalence and correlates among opioid-using people who inject drugs in Vancouver, Canada

BACKGROUND

Pain can return temporarily to old injury sites during opioid withdrawal. The prevalence and impact of opioid withdrawal-associated injury site pain (WISP) in various groups is unknown.

METHODS

Using data from observational cohorts, we estimated the prevalence and correlates of WISP among opioid-using people who inject drugs (PWID). Between June and December 2015, data on WISP and opioid use behaviours were elicited from participants in three ongoing prospective cohort studies in Vancouver, Canada, who were aged 18 years and older and who self-reported at least daily injection of heroin or non-medical presciption opioids.

RESULTS

Among 631 individuals, 276 (43.7 %) had a healed injury (usually pain-free), among whom 112 (40.6 %) experienced WISP, representing 17.7 % of opioid-using PWID interviewed. In a multivariable logistic regression model, WISP was positively associated with having a high school diploma or above (Adjusted Odds Ratio [AOR] = 2.23, 95 % Confidence Interval [CI]: 1.31-3.84), any heroin use in the last six months (AOR = 2.00, 95 % CI: 1.14-3.57), feeling daily pain that required medication (AOR = 2.06, CI: 1.18-3.63), and negatively associated with older age at first drug use (AOR = 0.96, 95 % CI: 0.93-0.99). Among 112 individuals with WISP, 79 (70.5 %) said that having this pain affected their opioid use behaviour, of whom 57 (72.2 %) used more opioids, 19 (24.1 %) avoided opioid withdrawal, while 3 (3.8 %) no longer used opioids to avoid WISP.

CONCLUSIONS

WISP is prevalent among PWID with a previous injury, and may alter opioid use patterns. Improved care strategies for WISP are warrented.

Ketorolac prevents recurrent withdrawal induced hyperalgesia but does not inhibit tolerance to spinal morphine in the rat

Chronic use of opioid is associated with pro-nociceptive phenomena such as hyperalgesia or tolerance. The interaction between opioid and non-steroidal anti-inflammatory drugs (NSAIDs) with respect to opioid-associated hyperalgesia and tolerance remains largely unknown. This study examines the effect of subcutaneous or intrathecal administration of ketorolac, an NSAID, on recurrent withdrawal induced hyperalgesia and tolerance to spinal morphine in rats. Animals were infused with morphine intrathecally, and daily subcutaneous naloxone was used for recurrent withdrawal purpose. We observed that escape latencies on hot box were decreased in animals subjected to withdrawal, and this decrease was reversed by subcutaneous ketorolac pretreatment. In addition, we observed that recurrent withdrawal did not significantly affect the magnitude of spinal morphine tolerance. Compared to controls, all morphine infused animals showed similar changes in their dose responses to spinal morphine, effective dose 50 values and tolerance ratios; and these changes were not affected by the ketorolac given subcutaneously. The effect of ketorolac on tolerance was further examined by directly delivering ketorolac to the spinal cord, and again we observed similar changes in the daily latency, percentage of area under the curve and percentage of maximal possible effects among groups infused with morphine, regardless of intrathecal ketorolac treatment. Together, our results demonstrate that recurrent withdrawal is associated with hyperalgesia but this has no effect on the tolerance development; ketorolac protects against recurrent withdrawal induced hyperalgesia without significantly altering spinal morphine tolerance.

Tolerance, opioid-induced allodynia and withdrawal associated allodynia in infant and young rats

Our laboratory has previously characterized age-dependent changes in nociception upon acute morphine withdrawal. This study characterizes changes in mechanical and thermal nociception following acute, intermittent, or continuous morphine administration in infant (postnatal days 5-8) and young (postnatal days 19-21) rats. Morphine was given as a single acute administration (AM), intermittently twice a day for 3 days (IM), or continuously for 72 h via pump (CM). AM did not produce long-term changes in mechanical or thermal nociception in either infant or young rats. CM produced changes in mechanical nociception that included the development of tolerance, opioid-induced mechanical allodynia and withdrawal-associated mechanical allodynia in young rats, but only tolerance and a prolonged withdrawal-associated mechanical allodynia in infant rats. IM produced withdrawal-associated mechanical allodynia in both infant and young rats. Measuring paw withdrawal responses to thermal stimuli, infant and young rats showed tolerance without opioid-induced thermal hyperalgesia or withdrawal-associated thermal hyperalgesia following CM. In contrast to CM, withdrawal-associated thermal hyperalgesia was seen in both ages following IM. In conclusion, CM versus IM differentially modified mechanical and thermal nociception, suggesting that opioid-dependent thermal hyperalgesia and mechanical allodynia can be dissociated from each other in infant and young rats. Furthermore, tolerance, opioid-induced hypersensitivity, and withdrawal-associated hypersensitivity are age-specific and may be mediated by distinct mechanisms.

Effects of recurrent withdrawal on spinal GABA release during chronic morphine infusion in the rat

Chronic opioid administration is associated with altered nociception. The mechanisms underlying these changes are not fully understood. Nociceptive transmission within the spinal cord is modulated by both excitatory and inhibitory neurotransmitters. Using spinal microdialysis, the effects of recurrent withdrawal on the release of gamma-aminobutyric acid (GABA), at rest or after naloxone stimulation, was investigated in rats chronically exposed to morphine. For comparison purpose, the release of glutamate was investigated in parallel. We observed that chronic morphine treatment alone significantly inhibited resting GABA release; and recurrent withdrawal appeared to reverse this effect. Recurrent withdrawal also significantly elevated resting glutamate levels. In addition, we observed that only acute withdrawal moderately increased stimulated GABA release. In contrast, both acute and recurrent withdrawal markedly increased stimulated glutamate release. These observed changes in GABA release offer direct evidence that GABA may contribute to the altered nociceptive response mediated by opioids.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).