Alterations in high-affinity binding characteristics and levels of opioids in invertebrate ganglia during aging: evidence for an opioid compensatory mechanism.

In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals.

Behavioral effects of opiates on the land snail Helix aspersa.

The terrestrial snail Helix aspersa appears to have an endogenous opiate system involved with regulating its locomotor activities as well as its responses to tactile stimulations. In animals which were repeatedly injected with the same dose of morphine, tolerance developed. Injection of the opiate antagonist, naloxone, resulted in a gradual reversal of the morphine induced behavioral characteristics.