MORPHINE DISRUPTS LONG-RANGE SYNCHRONY OF GAMMA-OSCILLATIONS IN HIPPOCAMPAL SLICES

Oscillations in neuronal population activity within the gamma frequenc y band (>25 Hz) have been correlated with cognition: Gamma oscillation s could bind together features of a sensory stimulus by generating syn chrony between discrete cortical areas [Eckhorn, R., Bauer, R., Jordan , W., Brosch, M., Kruse, W., Munk, M. & Reitboeck, H. J. (1989) Biol, Cybern. 60, 121-130; Singer, W. & Gray, C.;M. (1995) Annu. Rev. Neuros ci, 18, 555-556], Herein me demonstrate that morphine and beta-endorph in disrupt this long-range synchrony of gamma oscillations while leavi ng the synchrony of local oscillations relatively intact. The effect i s caused by a decrease in type A gamma-aminobutyric acid receptor-medi ated inhibition of both excitatory pyramidal cells and inhibitory inte rneurons, The effects of morphine on gamma oscillations were blocked b y mu-opioid receptor antagonists but not by antagonists of delta or ka ppa receptors, Morphine also produced burst firing in interneurons, be cause synaptic excitation from pyramidal cells was no longer balanced by synchronous inhibitory postsynaptic potentials, The loss of synchro ny of gamma oscillations induced by morphine may constitute one mechan ism involved in producing the cognitive deficits that this drug causes clinically.