Opioid enhancement of calcium oscillations and burst events involving NMDA receptors and L-type calcium channels in cultured hippocampal neurons.
Opioid receptor agonists are known to alter the activity of membrane ionic conductances and receptor-activated channels in CNS neurons and, via these mechanisms, to modulate neuronal excitability and synaptic transmission. In neuronal-like cell lines opioids also have been reported to induce intracellular Ca(2+) signals and to alter Ca(2+) signals evoked by membrane depolarization; these effects on intracellular Ca(2+) may provide an additional mechanism through which opioids modulate neuronal activity. However, opioid effects on resting or stimulated intracellular Ca(2+) levels have not been demonstrated in native CNS neurons. Thus, we investigated opioid effects on intracellular Ca(2+) in cultured rat hippocampal neurons by using fura-2-based microscopic Ca(2+) imaging. The opioid receptor agonist D-Ala(2)-N-Me-Phe(4),Gly-ol(5)-enkephalin (DAMGO; 1 microM) dramatically increased the amplitude of spontaneous intracellular Ca(2+) oscillations in the hippocampal neurons, with synchronization of the Ca(2+) oscillations across neurons in a given field. The effects of DAMGO were blocked by the opioid receptor antagonist naloxone (1 microM) and were dependent on functional NMDA receptors and L-type Ca(2+) channels. In parallel whole-cell recordings, DAMGO enhanced spontaneous, synaptically driven NMDA receptor-mediated burst events, depolarizing responses to exogenous NMDA and current-evoked Ca(2+) spikes. These results show that the activation of opioid receptors can augment several components of neuronal Ca(2+) signaling pathways significantly and, as a consequence, enhance intracellular Ca(2+) signals. These results provide evidence of a novel neuronal mechanism of opioid action on CNS neuronal networks that may contribute to both short- and long-term effects of opioids.
Przewlocki
R
R
Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037, USA.
Parsons
K L
KL
Sweeney
D D
DD
Trotter
C
C
Netzeband
J G
JG
Siggins
G R
GR
Gruol
D L
DL
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006624:Hippocampus / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009553:Nimodipine / Q000494:pharmacology; D009991:Oscillometry; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D011957:Receptors, Opioid / Q000819:agonists; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
D020746:Calcium Channels, L-Type; D018691:Excitatory Amino Acid Antagonists; D011810:Quinoxalines; D016194:Receptors, N-Methyl-D-Aspartate; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D013779:Tetrodotoxin; D009553:Nimodipine; C056723:FG 9041; D015763:2-Amino-5-phosphonovalerate; D002118:Calcium