Effects of intracerebral morphine and enkephalins on the caudate-EEG spindle burst

In an attempt to study the neural mechanisms of generation of the caudate-EEG spindle burst, effects of morphine, met-enkephalin and leu-enkephalin on the spindle were studied in gallamine-immobilized rats. The "caudate spindle" was significantly enhanced by microinjections of morphine and enkephalins into the lateral ventriculus, the thalamus, the midbrain reticular formation and the hippocampus but not the caudate nucleus, and the effects of these agents were completely antagonized by prior administration of naloxone. Intravenously administered morphine showed inhibitory actions on the neurons in the thalamus and the reticular formation and an excitatory effect on the hippocampal neurons. These results suggest that the enkephalinergic system may play an important role in the generation of the caudate spindle in the rat, i.e. as a positive modulatory system in the manifestation of the caudate spindle.