Exogenous nerve growth factor attenuates opioid-induced inhibition of voltage-activated Ba2+ currents in rat sensory neurons

Abstract

Nerve growth factor (NGF) promotes the survival of embryonic sensory neurons and maintains the phenotypic characteristics of primary nociceptive neurons postnatally. NGF also contributes to nociceptor activation and hyperalgesia during inflammatory pain states. The purpose of this study was to determine whether NGF might have an additional pronociceptive action by interfering with opioid-mediated analgesia in primary nociceptive neurons. Sensory neurons were isolated from the dorsal root ganglia of weanling rats and kept in standard culture conditions either with or without exogenous NGF (50 ng/ml). Currents through voltage-gated calcium channels were recorded from individual neurons using the whole cell patch clamp technique with Ba 2+ as the charge carrier (I Ba ). The μ-opioid agonist fentanyl (1 μM) and the GABA B agonist baclofen (50 μM) were used to test G protein-dependent inhibition of I Ba . Fentanyl inhibited I Ba by an average of 38±4% in untreated cells vs. 25±2% in NGF-treated cells (P<0.01). NGF had no effect on I Ba current magnitude or kinetics. The NGF-induced attenuation of opioid action was observed as early as 4 h after exposure, but was not seen when NGF was applied by bath perfusion for up to 40 min, suggesting that the effect was not mediated by a rapid phosphorylation event. The effect of NGF was prevented by K-252a (100 nM), an inhibitor of TrkA autophosphorylation. Baclofen-induced inhibition of I Ba , on the other hand, was not affected by NGF treatment, suggesting that NGF modulation of opioid-mediated inhibition occurred upstream from the G protein. This was supported by the finding that GTP-γ-S, an agonist independent G protein activator, inhibited I Ba similarly in both untreated and NGF treated cells. The results show that NGF selectively attenuated opioid-mediated inhibition of I Ba via TrkA receptor activation, possibly by altering opioid receptor function. Keywords neurotrophins; DRG neurons; G proteins; patch clampNerve growth factor (NGF) is a neurotrophin required for the survival of most primary nociceptive neurons during embryonic development. A large number of nociceptive neurons remain sensitive to NGF postnatally, and in adult animals NGF plays a role in both physiological and pathological pain conditions. In the resting state, low levels of NGF are needed for the expression of nociceptor markers such as the neuropeptides substance P and calcitonin-gene-related peptide (CGRP; Molliver and Snider, 1997;Patel et al., 2000), and for nociceptive afferents to retain their ability to respond to noxious stimuli (Ritter et al., 1991;Lewin and Mendell, 1994;McMahon et al., 1995;Bennett et al., 1998 (Donnerer et al., 1992;Woolf et al., 1994;McMahon et al., 1995;Koltzenburg et al., 1999).NGF may sensitize nociceptors in several ways. NGF has been shown to upregulate the TRPV1 channel, one of the molecular transducers of noxious heat which is also activated by capsaicin, and to increase capsaicin-induced currents in nociceptors (Nicholas et al., 1999;Shu and Mendell, 2001;J...

The function neutralizing anti-TrkA antibody MNAC13 reduces inflammatory and neuropathic pain

“…Previous evidence showed a negative interaction between opiates and NGF signaling pathways in primary sensory neurons (34). Conversely, the inflammation-related increase of NGF induced by carrageenan is attenuated by morphine (35).…”

“…In addition, because a functional interaction between NGF and opioid system was reported in experimental models of inflammatory pain (34,35), the possible synergistic effects of the anti-TrkA antibody with opiates, such as morphine and fentanyl, were investigated.…”

Effect of transdermal opioids in experimentally induced superficial, deep and hyperalgesic pain

“…2003; Andersen et al ., 2008) we found NGF induced sensitization in the placebo arm within the first 72 h after injection and was most prominent after 24 h. In our study it was not possible to show an analgesic effect to pressure after intramuscular injection of NGF even though a sensitization was present. Animal studies suggest that NGF interferes with nociceptive neurons and attenuates the analgesic effects of opioids (McDowell, 2004; Mousa et al . 2007), which could have influenced the analgesic effects of the drugs in the present study.…”

The roles of nerve growth factor and cholecystokinin in the enhancement of morphine analgesia in a rodent model of central nervous system inflammation

“…However, we did find enhanced morphine analgesia in rats that had been treated with chronic NGF. This may be explained by evidence from recent studies suggesting that NGF can directly influence opioid receptors in-vitro, in transgenic animals, or in inflammatory pain models (McDowell, 2004;Molliver et al, 2005;Mousa et al, 2007). Alternatively, numerous studies show that chronic systemic or intrathecal NGF administration results in multiple changes in neuropeptides involved in nociception (Malcangio et al, 1997;Malcangio et al, 2000;Jongsma Wallin et al, 2001;Ramer et al, 2001;Bowles et al, 2004) and potentially in morphine sensitivity.…”