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The effect of opiate drugs on the caudate spindle (CS) in the cat was observed following both systemic and intracaudal administration. Systemic administration of morphine, pentazocine and pethidine inhibited the CS. The inhibitory effects of opiates were antagonized by lysergide and methysergide but not by naloxone, chlorpromazine, dehydrobenzperidol, amphetamine and atropine. Contrary to their systemic administration, the investigated opiates morphine, pentazocine, pethidine and Met⁵-Enkephaline enhanced the CS, when injected into the caudate nucleus close to the site of stimulation. Those facilitating effects of opiates on the CS were completely blocked by naloxone. The results suggest that serotoninergic mechanisms might be involved in the action of opiates on the neuronal activity of the caudate nucleus.

The previously suggested opiate-receptor antagonistic properties of compound 48/80 were checked both in vivo and in vitro. In electrically stimulated guinea pig ileum and rat vas deferens preparations compound 48/80 did not reverse the inhibition of the twitches caused either by morphine or Met⁵-enkephalin. In mice hot-plate test compound 48/80 did not decrease the analgesic activity of morphine. In radioreceptor studies compound 48/80 shows rather low affinity to the ³H-naloxone receptor sites from striatal homogenates of the rat, as compared to non-labelled naloxone and on the other hand it produced moderate, as compared to d-butaclamol, displacement of ³H-spiroperidol from rat striatal homogenates. The variation of composition of various polymers making compound 48/80 is suggested for explanation of obtained results.