CHRONIC OPIOID TREATMENT OF NEUROBLASTOMA X DORSAL-ROOT GANGLION NEURON HYBRID F11 CELLS RESULTS IN ELEVATED GM1 GANGLIOSIDE AND CYCLIC ADENOSINE-MONOPHOSPHATE LEVELS AND ONSET OF NALOXONE-EVOKED DECREASES IN MEMBRANE K+ CURRENTS

Prolongation of the action potential duration of dorsal root ganglion (DRG) neurons by low (nM) concentrations of opioids occurs through activation of excitatory opioid receptors that are positively coupled via G(s) regulatory protein to adenylate cyclase. Previous results suggested GM1 ganglioside to have an essential role in regulating this excitatory response, but not the inhibitory (APD-shortening) response to higher (mu M) opioid concentrations. Furthermore, it was proposed that synthesis of GM1 is upregulated by prolonged activation of excitatory opioid receptor functions. To explore this possibility we have utilized cultures of hybrid F11 cells to carry out closely correlated electrophysiological and biochemical analyses of the effects of chronic opioid treatment on a homogeneous population of clonal cells which express many functions characteristic of DRG neurons. We show that chronic opioid exposure of F11 cells does, in fact, result in elevated levels of GM1 as well as cyclic adenosine monophosphate (AMP), concomitant with the onset of opioid excitatory supersensitivity as manifested by naloxone-evoked decreases in voltage-dependent membrane K+ currents. Such elevation of GM1 would be expected to enhance the efficacy of excitatory opioid receptor activation of the G(s)/adenylate cyclase/cyclic AMP system, thereby providing a positive feedback mechanism that may account for the remarkable supersensitivity of chronic opioid-treated neurons to the excitatory effects of opioid agonists as well as antagonists. These in vitro findings may provide novel insights into the mechanisms underlying naloxone-precipitated withdrawal syndromes and opioid-induced hyperalgesia after chronic opiate addiction in vivo. (C) 1995 Wiley-Liss, Inc.